Encryption

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Encryption 

A simple illustration of public-key cryptography, one of the most widely used form of encryption

In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can decipher a ciphertext back to plaintext and access the original information. Encryption does not itself prevent interference but denies the intelligible content to a would-be interceptor.

For technical reasons, an encryption scheme usually uses a pseudo-random encryption key generated by an algorithm. It is possible to decrypt the message without possessing the key but, for a well-designed encryption scheme, considerable computational resources and skills are required. An authorized recipient can easily decrypt the message with the key provided by the originator to recipients but not to unauthorized users.

Historically, various forms of encryption have been used to aid in cryptography. Early encryption techniques were often used in military messaging. Since then, new techniques have emerged and become commonplace in all areas of modern computing. Modern encryption schemes use the concepts of public-key and symmetric-key. Modern encryption techniques ensure security because modern computers are inefficient at cracking the encryption.

History

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Ancient

One of the earliest forms of encryption is symbol replacement, which was first found in the tomb of Khnumhotep II, who lived in 1900 BC Egypt. Symbol replacement encryption is “non-standard,” which means that the symbols require a cipher or key to understand. This type of early encryption was used throughout Ancient Greece and Rome for military purposes. One of the most famous military encryption developments was the Caesar Cipher, which was a system in which a letter in normal text is shifted down a fixed number of positions down the alphabet to get the encoded letter. A message encoded with this type of encryption could be decoded with the fixed number on the Caesar Cipher.

Around 800 AD, Arab mathematician Al-Kindi developed the technique of frequency analysis – which was an attempt to systematically crack Caesar ciphers. This technique looked at the frequency of letters in the encrypted message to determine the appropriate shift. This technique was rendered ineffective after the creation of the Polyalphabetic cipher by Leone Alberti in 1465, which incorporated different sets of languages. In order for frequency analysis to be useful, the person trying to decrypt the message would need to know which language the sender chose.

19th–20th century

Around 1790, Thomas Jefferson theorised a cipher to encode and decode messages in order to provide a more secure way of military correspondence. The cipher, known today as the Wheel Cipher or the Jefferson Disk, although never actually built, was theorized as a spool that could jumble an English message up to 36 characters. The message could be decrypted by plugging in the jumbled message to a receiver with an identical cipher.

A similar device to the Jefferson Disk, the M-94, was developed in 1917 independently by US Army Major Joseph Mauborne. This device was used in U.S. military communications until 1942.

In World War II, the Axis powers used a more advanced version of the M-94 called the Enigma Machine. The Enigma Machine was more complex because unlike the Jefferson Wheel and the M-94, each day the jumble of letters switched to a completely new combination. Each day's combination was only known by the Axis, so many thought the only way to break the code would be to try over 17,000 combinations within 24 hours. The Allies used computing power to severely limit the number of reasonable combinations they needed to check every day, leading to the breaking of the Enigma Machine.

Modern

Today, encryption is used in the transfer of communication over the Internet for security and commerce. As computing power continues to increase, computer encryption is constantly evolving to prevent eavesdropping attacks. With one of the first “modern” cipher suits, DES, utilizing a 56-bit key with 72,057,594,037,927,936 possibilities being able to be cracked in 22 hours and 15 minutes by EFF’s DES cracker in 1999, which used a brute-force method of cracking. Modern encryption standards often use stronger key sizes often 256, like AES(256-bit mode), TwoFish, ChaCha20-Poly1305, Serpent(configurable up to 512-bit). Cipher suits utilizing a 128-bit or higher key, like AES, will not be able to be brute-forced due to the total amount of keys of 3.4028237e+38 possibilities. The most likely option for cracking ciphers with high key size is to find vulnerabilities in the cipher itself, like inherent biases and backdoors. For example, RC4, a stream cipher was cracked due to inherit biases and vulnerabilities in the cipher.

Encryption in cryptography

In the context of cryptography, encryption serves as a mechanism to ensure confidentiality. Since data may be visible on the Internet, sensitive information such as passwords and personal communication may be exposed to potential interceptors. The process of encrypting and decrypting messages involves keys. The two main types of keys in cryptographic systems are symmetric-key and public-key (also known as asymmetric-key).

Many complex cryptographic algorithms often use simple modular arithmetic in their implementations.

Types

In symmetric-key schemes, the encryption and decryption keys are the same. Communicating parties must have the same key in order to achieve secure communication. The German Enigma Machine utilized a new symmetric-key each day for encoding and decoding messages.

In public-key encryption schemes, the encryption key is published for anyone to use and encrypt messages. However, only the receiving party has access to the decryption key that enables messages to be read. Public-key encryption was first described in a secret document in 1973; beforehand, all encryption schemes were symmetric-key (also called private-key). Although published subsequently, the work of Diffie and Hellman was published in a journal with a large readership, and the value of the methodology was explicitly described. The method became known as the Diffie-Hellman key exchange.

RSA (Rivest–Shamir–Adleman) is another notable public-key cryptosystem. Created in 1978, it is still used today for applications involving digital signatures. Using number theory, the RSA algorithm selects two prime numbers, which help generate both the encryption and decryption keys.

A publicly available public-key encryption application called Pretty Good Privacy (PGP) was written in 1991 by Phil Zimmermann, and distributed free of charge with source code. PGP was purchased by Symantec in 2010 and is regularly updated.

Uses

Encryption has long been used by militaries and governments to facilitate secret communication. It is now commonly used in protecting information within many kinds of civilian systems. For example, the Computer Security Institute reported that in 2007, 71% of companies surveyed utilized encryption for some of their data in transit, and 53% utilized encryption for some of their data in storage. Encryption can be used to protect data "at rest", such as information stored on computers and storage devices (e.g. USB flash drives). In recent years, there have been numerous reports of confidential data, such as customers' personal records, being exposed through loss or theft of laptops or backup drives; encrypting such files at rest helps protect them if physical security measures fail. Digital rights management systems, which prevent unauthorized use or reproduction of copyrighted material and protect software against reverse engineering (see also copy protection), is another somewhat different example of using encryption on data at rest.

Encryption is also used to protect data in transit, for example data being transferred via networks (e.g. the Internet, e-commerce), mobile telephones, wireless microphones, wireless intercom systems, Bluetooth devices and bank automatic teller machines. There have been numerous reports of data in transit being intercepted in recent years. Data should also be encrypted when transmitted across networks in order to protect against eavesdropping of network traffic by unauthorized users.

Data erasure

Main article: Data erasure

Conventional methods for permanently deleting data from a storage device involve overwriting the device's whole content with zeros, ones, or other patterns – a process which can take a significant amount of time, depending on the capacity and the type of storage medium. Cryptography offers a way of making the erasure almost instantaneous. This method is called crypto-shredding. An example implementation of this method can be found on iOS devices, where the cryptographic key is kept in a dedicated 'effaceable storage'. Because the key is stored on the same device, this setup on its own does not offer full privacy or security protection if an unauthorized person gains physical access to the device.

Limitations

Encryption is used in the 21st century to protect digital data and information systems. As computing power increased over the years, encryption technology has only become more advanced and secure. However, this advancement in technology has also exposed a potential limitation of today's encryption methods.

The length of the encryption key is an indicator of the strength of the encryption method. For example, the original encryption key, DES (Data Encryption Standard), was 56 bits, meaning it had 2^56 combination possibilities. With today's computing power, a 56-bit key is no longer secure, being vulnerable to hacking by brute force attack. Today the standard of modern encryption keys is up to 2048 bit with the RSA system. Decrypting a 2048 bit encryption key is nearly impossible in light of the number of possible combinations. However, quantum computing is threatening to change this secure nature.

Quantum computing utilizes properties of quantum mechanics in order to process large amounts of data simultaneously. Quantum computing has been found to achieve computing speeds thousands of times faster than today's supercomputers. This computing power presents a challenge to today's encryption technology. For example, RSA encryption utilizes the multiplication of very large prime numbers to create a semiprime number for its public key. Decoding this key without its private key requires this semiprime number to be factored in, which can take a very long time to do with modern computers. It would take a supercomputer anywhere between weeks to months to factor in this key. However, quantum computing can use quantum algorithms to factor this semiprime number in the same amount of time it takes for normal computers to generate it. This would make all data protected by current public-key encryption vulnerable to quantum computing attacks. Other encryption techniques like elliptic curve cryptography and symmetric key encryption are also vulnerable to quantum computing.

While quantum computing could be a threat to encryption security in the future, quantum computing as it currently stands is still very limited. Quantum computing currently is not commercially available, cannot handle large amounts of code, and only exists as computational devices, not computers. Furthermore, quantum computing advancements will be able to be utilized in favor of encryption as well. The National Security Agency (NSA) is currently preparing post-quantum encryption standards for the future. Quantum encryption promises a level of security that will be able to counter the threat of quantum computing.

Attacks and countermeasures

Encryption is an important tool but is not sufficient alone to ensure the security or privacy of sensitive information throughout its lifetime. Most applications of encryption protect information only at rest or in transit, leaving sensitive data in clear text and potentially vulnerable to improper disclosure during processing, such as by a cloud service for example. Homomorphic encryption and secure multi-party computation are emerging techniques to compute on encrypted data; these techniques are general and Turing complete but incur high computational and/or communication costs.

In response to encryption of data at rest, cyber-adversaries have developed new types of attacks. These more recent threats to encryption of data at rest include cryptographic attacks, stolen ciphertext attacks, attacks on encryption keys, insider attacks, data corruption or integrity attacks, data destruction attacks, and ransomware attacks. Data fragmentation and active defense data protection technologies attempt to counter some of these attacks, by distributing, moving, or mutating ciphertext so it is more difficult to identify, steal, corrupt, or destroy.

Integrity protection of ciphertexts

Encryption, by itself, can protect the confidentiality of messages, but other techniques are still needed to protect the integrity and authenticity of a message; for example, verification of a message authentication code (MAC) or a digital signature usually done by a hashing algorithm or a PGP signature. Authenticated encryption algorithms are designed to provide both encryption and integrity protection together. Standards for cryptographic software and hardware to perform encryption are widely available, but successfully using encryption to ensure security may be a challenging problem. A single error in system design or execution can allow successful attacks. Sometimes an adversary can obtain unencrypted information without directly undoing the encryption. See for example traffic analysis, TEMPEST, or Trojan horse.

Integrity protection mechanisms such as MACs and digital signatures must be applied to the ciphertext when it is first created, typically on the same device used to compose the message, to protect a message end-to-end along its full transmission path; otherwise, any node between the sender and the encryption agent could potentially tamper with it. Encrypting at the time of creation is only secure if the encryption device itself has correct keys and has not been tampered with. If an endpoint device has been configured to trust a root certificate that an attacker controls, for example, then the attacker can both inspect and tamper with encrypted data by performing a man-in-the-middle attack anywhere along the message's path. The common practice of TLS interception by network operators represents a controlled and institutionally sanctioned form of such an attack, but countries have also attempted to employ such attacks as a form of control and censorship.

Ciphertext length and padding

Main article: Padding (cryptography)

Even when encryption correctly hides a message's content and it cannot be tampered with at rest or in transit, a message's length is a form of metadata that can still leak sensitive information about the message. For example, the well-known CRIME and BREACH attacks against HTTPS were side-channel attacks that relied on information leakage via the length of encrypted content. Traffic analysis is a broad class of techniques that often employs message lengths to infer sensitive implementation about traffic flows by aggregating information about a large number of messages.

Padding a message's payload before encrypting it can help obscure the cleartext's true length, at the cost of increasing the ciphertext's size and introducing or increasing bandwidth overhead. Messages may be padded randomly or deterministically, with each approach having different tradeoffs. Encrypting and padding messages to form padded uniform random blobs or PURBs is a practice guaranteeing that the cipher text leaks no metadata about its cleartext's content, and leaks asymptotically minimal ${\displaystyle O(\log \log M)}$ information via its length.

Centaur (rocket stage)

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Centaur_(rocket_stage) 

 

Centaur III

A single-engine Centaur III being raised for mating to an Atlas V rocket
Manufacturer	United Launch Alliance
Used on	Atlas V: Centaur III Vulcan: Centaur V Titan IV Space Shuttle: Shuttle-Centaur (cancelled due to Challenger disaster)
General characteristics
Height	12.68 m (499 in)
Diameter	3.05 m (120 in)
Propellant mass	20,830 kg (45,920 lb)
Empty mass	2,247 kg (4,954 lb), single engine 2,462 kg (5,428 lb), dual engine
Centaur III
Powered by	1 or 2 RL10
Maximum thrust	99.2 kN (22,300 lbf), per engine
Specific impulse	450.5 seconds (4.418 km/s)
Burn time	Variable
Propellant	LH2 / LOX
Associated stages
Derivatives	Centaur V Advanced Cryogenic Evolved Stage
Launch history
Status	Active
Total launches	245 as of January 2018
First flight	May 9, 1962

A dual engine Centaur stage

 

Centaur stage during assembly at General Dynamics, 1962

 

Diagram of the Centaur stage tank

The Centaur is a family of rocket propelled upper stages produced by U.S. launch service provider United Launch Alliance, with one main active version and one version under development. The 3.05 m (10.0 ft) diameter Common Centaur/Centaur III flies as the upper stage of the Atlas V launch vehicle, and the 5.4 m (18 ft) diameter Centaur V is being developed as the upper stage of ULA's new Vulcan rocket. Centaur was the first rocket stage to use liquid hydrogen (LH₂) and liquid oxygen (LOX) propellants, a high-energy combination that is ideal for upper stages but has significant handling difficulties.

Characteristics

Common Centaur is built around stainless steel pressure stabilized balloon propellant tanks with 0.51 mm (0.020 in) thick walls. It can lift payloads of up to 19,000 kg (42,000 lb). The thin walls minimize the mass of the tanks, maximizing the stage's overall performance.

A common bulkhead separates the LOX and LH₂ tanks, further reducing the tank mass. It is made of two stainless steel skins separated by a fiberglass honeycomb. The fiberglass honeycomb minimizes heat transfer between the extremely cold LH₂ and relatively warm LOX.

The main propulsion system consists of one or two Aerojet Rocketdyne RL10 engines. The stage is capable of up to twelve restarts, limited by propellant, orbital lifetime, and mission requirements. Combined with the insulation of the propellant tanks, this allows Centaur to perform the multi-hour coasts and multiple engine burns required on complex orbital insertions.

The reaction control system (RCS) also provides ullage and consists of twenty hydrazine monopropellant engines located around the stage in two 2-thruster pods and four 4-thruster pods. For propellant, 150 kg (340 lb) of Hydrazine is stored in a pair of bladder tanks and fed to the RCS engines with pressurized helium gas, which is also used to accomplish some main engine functions.

Current versions

As of 2019, all but two of the many Centaur variants had been retired: Common Centaur/Centaur III (active) and Centaur V (in development).

Current engines

Version	Stage used on	Dry mass	Thrust	Isp, vac.	Length	Diameter
RL10A-4-2	Centaur III (DEC)	168 kg (370 lb)	99.1 kN (22,300 lbf)	451 s		1.17 m (3.8 ft)
RL10C-1	Centaur III (SEC), (DCSS)	190 kg (420 lb)	101.8 kN (22,900 lbf)	449.7 s	2.12 m (7.0 ft)	1.45 m (4.8 ft)
RL10C-1-1	Centaur V	188 kg (414 lb)	106 kN (24,000 lbf)	453.8 s	2.46 m (8.1 ft)	1.57 m (5.2 ft)

Centaur III/Common Centaur

Common Centaur is the upper stage of the Atlas V rocket. Earlier Common Centaurs were propelled by the RL10-A-4-2 version of the RL-10. Since 2014, Common Centaur has flown with the RL10-C-1 engine, which is shared with the Delta Cryogenic Second Stage, to reduce costs. The Dual Engine Centaur (DEC) configuration will continue to use the smaller RL10-A-4-2 to accommodate two engines in the available space.

The Atlas V can fly in multiple configurations, but only one affects the way Centaur integrates with the booster and fairing: the 5.4 m (18 ft) diameter Atlas V payload fairing attaches to the booster and encapsulates the upper stage and payload, routing fairing-induced aerodynamic loads into the booster. If the 4 m (13 ft) diameter payload fairing is used, the attachment point is at the top (forward end) of Centaur, routing loads through the Centaur tank structure.

The latest Common Centaurs can accommodate secondary payloads using an Aft Bulkhead Carrier attached to the engine end of the stage.

Single Engine Centaur (SEC)

Most payloads launch on Single Engine Centaur (SEC) with one RL10. This is the variant for all normal flights of the Atlas V (indicated by the last digit of the naming system, for example Atlas V 421).

Dual Engine Centaur (DEC)

A dual engine variant with two RL-10 engines is available, but only in use to launch the CST-100 Starliner crewed spacecraft and possibly the Dream Chaser ISS logistics spaceplane. The higher thrust of two engines allows a gentler ascent with more horizontal velocity and less vertical velocity, which reduces deceleration to survivable levels in the event of a launch abort and ballistic reentry occurring at any point in the flight.

Centaur V

Centaur V will be the upper stage of the new Vulcan launch vehicle currently being developed by the United Launch Alliance to meet the needs of the National Security Space Launch (NSSL) program. Vulcan was initially intended to enter service with an upgraded variant of the Common Centaur, with an upgrade to the Advanced Cryogenic Evolved Stage (ACES) planned after the first few years of flights.

In late 2017, ULA decided to bring elements of the ACES upper stage forward and begin work on Centaur V. Centaur V will have ACES' 5.4 m (18 ft) diameter and advanced insulation, but does not include the Integrated Vehicle Fluids (IVF) feature expected to allow the extension of upper stage on-orbit life from hours to weeks. Centaur V will use 2 different versions of the RL10-C engine with nozzle extensions to improve the fuel consumption for the heaviest payloads. This increased capability over Common Centaur will permit ULA to meet NSSL requirements and retire both the Atlas V and Delta IV Heavy rocket families earlier than initially planned. The new rocket publicly became the Vulcan Centaur in March 2018. In May 2018, the Aerojet Rocketdyne RL10 was announced as Centaur V's engine following a competitive procurement process against the Blue Origin BE-3. Each stage will mount two engines. In September 2020, ULA announced that ACES was no longer being developed, and that Centaur V would be used instead. Tory Bruno, ULA's CEO, stated that the Vulcan’s Centaur 5 will have 40% more endurance and two and a half times more energy than the upper stage ULA currently flies. “But that’s just the tip of the iceberg,” Bruno elaborated. “I’m going to be pushing up to 450, 500, 600 times the endurance over just the next handful of years. That will enable a whole new set of missions that you cannot even imagine doing today.”

History

The Centaur concept originated in 1956 when Convair began studying a liquid hydrogen fueled upper stage. The ensuing project began in 1958 as a joint venture among Convair, the Advanced Research Projects Agency (ARPA), and the U.S. Air Force. In 1959, NASA assumed ARPA's role. Centaur initially flew as the upper stage of the Atlas-Centaur launch vehicle, encountering a number of early developmental issues due to the pioneering nature of the effort and the use of liquid hydrogen. In 1994 General Dynamics sold their Space Systems division to Lockheed-Martin.

Centaur A-D (Atlas)

An Atlas-Centaur rocket launches Surveyor 1

 

Main article: Atlas-Centaur

The Centaur was originally developed for use with the Atlas launch vehicle family. Known in early planning as the 'high-energy upper stage', the choice of the mythological Centaur as a namesake was intended to represent the combination of the brute force of the Atlas booster and finesse of the upper stage.

Initial Atlas-Centaur launches used developmental versions, labeled Centaur-A through -C. The only Centaur-A launch on 8 May 1962 ended in an explosion 54 seconds after liftoff when insulation panels on the Centaur separated early, causing the LH₂ tank to overheat and rupture. After extensive redesigns, the only Centaur-B flight on 26 November 1963 was successful. Centaur-C flew three times with two failures and one launch declared successful although the Centaur failed to restart. Centaur-D was the first version to enter operational service, with fifty-six launches.

On 30 May 1966, an Atlas-Centaur boosted the first Surveyor lander towards the Moon. This was followed by six more Surveyor launches over the next two years, with the Atlas-Centaur performing as expected. The Surveyor program demonstrated the feasibility of reigniting a hydrogen engine in space and provided information on the behavior of LH₂ in space.

By the 1970s, Centaur was fully mature and had become the standard rocket stage for launching larger civilian payloads into high Earth orbit, also replacing the Atlas-Agena vehicle for NASA planetary probes.

By the end of 1989, Centaur-D and -G had been used as the upper stage for 63 Atlas rocket launches, 55 of which were successful.

Saturn I S-V

Main article: S-V

 

A Saturn I launches with a ballasted S-V stage

The Saturn I was designed to fly with a S-V third stage to enable payloads to go beyond low earth orbit (LEO). The S-V stage was intended to be powered by two RL-10A-1 engines burning liquid hydrogen as fuel and liquid oxygen as oxidizer. The S-V stage was flown four times on missions SA-1 through SA-4, all four of these missions had the S-V's tanks filled with water to be used a ballast during launch. The stage was not flown in an active configuration.

Centaur D-1T (Titan III)

A Titan IIIE-Centaur rocket launches Voyager 2

The Centaur D was improved for use on the far more powerful Titan III booster in the 1970s, with the first launch of the resulting Titan IIIE in 1974. The Titan IIIE more than tripled the payload capacity of Atlas-Centaur, and incorporated improved thermal insulation, allowing an orbital lifespan of up to five hours, an increase over the 30 minutes of the Atlas-Centaur.

The first launch of Titan IIIE in February 1974 was unsuccessful, with the loss of the Space Plasma High Voltage Experiment (SPHINX) and a mockup of the Viking probe. It was eventually determined that Centaur's engines had ingested an incorrectly installed clip from the oxygen tank.

The next Titan-Centaurs launched Helios 1, Viking 1, Viking 2, Helios 2, Voyager 1, and Voyager 2. The Titan booster used to launch Voyager 1 had a hardware problem that caused a premature shutdown, which the Centaur stage detected and successfully compensated for. Centaur ended its burn with less than 4 seconds of fuel remaining.

Centaur (Atlas G)

Centaur was introduced on the Atlas G and was carried over to the very similar Atlas I.

Shuttle-Centaur (Centaur G and G-Prime)

Main article: Shuttle-Centaur

 

Illustration of Shuttle-Centaur with Ulysses

Shuttle-Centaur was a proposed Space Shuttle upper stage. To enable its installation in shuttle payload bays, the diameter of the Centaur's hydrogen tank was increased to 4.3 m (14 ft), with the LOX tank diameter remaining at 3.0 m (10 ft). Two variants were proposed: Centaur G Prime, which was planned to launch the Galileo and Ulysses robotic probes, and Centaur G, a shortened version, reduced in length from approximately 9 to 6 m (30 to 20 ft), planned for U.S. DoD payloads and the Magellan Venus probe.

After the Space Shuttle Challenger accident, and just months before the Shuttle-Centaur had been scheduled to fly, NASA concluded that it was too risky to fly the Centaur on the Shuttle. The probes were launched with the much less powerful solid-fueled IUS, with Galileo needing multiple gravitational assists from Venus and Earth to reach Jupiter.

Centaur (Titan IV)

The capability gap left by the termination of the Shuttle-Centaur program was filled by a new launch vehicle, the Titan IV. The 401A/B versions used a Centaur upper stage with a 4.3-meter (14 ft) diameter hydrogen tank. In the Titan 401A version, a Centaur-T was launched nine times between 1994 and 1998. The 1997 Cassini-Huygens Saturn probe was the first flight of the Titan 401B, with an additional six launches wrapping up in 2003 including one SRB failure.

Centaur II (Atlas II/III)

Main article: Atlas II

Centaur II was initially developed for use on the Atlas II series of rockets. Centaur II also flew on the initial Atlas IIIA launches.

Centaur III/Common Centaur (Atlas III/V)

Main article: Atlas III

Atlas IIIB introduced the Common Centaur, a longer and initially dual engine Centaur II.

Atlas V cryogenic fluid management experiments

Most Common Centaurs launched on Atlas V have hundreds to thousands of kilograms of propellants remaining on payload separation. In 2006 these propellants were identified as a possible experimental resource for testing in-space cryogenic fluid management techniques.

In October 2009, the Air Force and United Launch Alliance (ULA) performed an experimental demonstration on the modified Centaur upper stage of DMSP-18 launch to improve "understanding of propellant settling and slosh, pressure control, RL10 chilldown and RL10 two-phase shutdown operations. DMSP-18 was a low mass payload, with approximately 28% (5,400 kg (11,900 lb)) of LH₂/LOX propellant remaining after separation. Several on-orbit demonstrations were conducted over 2.4 hours, concluding with a deorbit burn. The initial demonstration was intended to prepare for more-advanced cryogenic fluid management experiments planned under the Centaur-based CRYOTE technology development program in 2012–2014, and will increase the TRL of the Advanced Cryogenic Evolved Stage Centaur successor.

Mishaps

Although Centaur has a long and successful flight history, it has experienced a number of mishaps:

• April 7, 1966: Centaur did not restart after coast — ullage motors ran out of fuel.
• May 9, 1971; Centaur guidance failed, destroying itself and the Mariner 8 spacecraft bound for Mars orbit.
• April 18, 1991: Centaur failed due to particles from the scouring pads used to clean the propellant ducts getting stuck in the turbopump, preventing start-up.
• August 22, 1992: Centaur failed to restart (icing problem).
• April 30, 1999: Launch of the USA-143 (Milstar DFS-3m) communications satellite failed when a Centaur database error resulted in uncontrolled roll rate and loss of attitude control, placing the satellite in a useless orbit.
• June 15, 2007: the engine in the Centaur upper stage of an Atlas V shut down early, leaving its payload — a pair of National Reconnaissance Office ocean surveillance satellites — in a lower than intended orbit. The failure was called "A major disappointment," though later statements claim the spacecraft will still be able to complete their mission. The cause was traced to a stuck-open valve that depleted some of the hydrogen fuel, resulting in the second burn terminating four seconds early. The problem was fixed, and the next flight was nominal.
• August 30, 2018: Atlas V Centaur passivated second stage launched on September 17, 2014 broke up, creating space debris.
• March 23–25, 2018: Atlas V Centaur passivated second stage launched on September 8, 2009 broke up.
• April 6, 2019: Atlas V Centaur passivated second stage launched on October 17, 2018 broke up.

Centaur III specifications

Source: Atlas V551 specifications, as of 2015.

• Diameter: 3.05 m (10 ft)
• Length: 12.68 m (42 ft)
• Inert mass: 2,247 kg (4,954 lb)
• Fuel: Liquid hydrogen
• Oxidizer: Liquid oxygen
• Fuel and oxidizer mass: 20,830 kg (45,922 lb)
• Guidance: Inertial
• Thrust: 99.2 kN (22,300 lbf)
• Burn time: Variable; e.g., 842 seconds on Atlas V
• Engine: RL10-C-1
• Engine length: 2.32 m (7.6 ft)
• Engine diameter: 1.53 m (5 ft)
• Engine dry weight: 168 kg (370 lb)
• Engine start: Restartable
• Attitude control: 4 27-N thrusters, 8 40-N thrusters
  • Propellant: Hydrazine

Dragonfly (spacecraft)

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Dragonfly_(spacecraft) 

Dragonfly

Spacecraft concept illustration
Mission type	Rotorcraft on Titan
Operator	NASA
COSPAR ID
Website	https://dragonfly.jhuapl.edu/
Mission duration	10 years (planned) Science phase: 3.3 years
Spacecraft properties
Spacecraft type	Rotorcraft lander
Manufacturer	Applied Physics Laboratory
Landing mass	≈450 kg (990 lb)
Power	70 watts (desired) from an MMRTG
Start of mission
Launch date	June 2027 (planned)
Rocket	Atlas V 411 or equivalent performance (actual launch vehicle will be selected later)
Launch site	TBA
Contractor	TBA
Titan aircraft
Landing date	2034
Landing site	Shangri-La dune fields
Distance flown	8 km (5.0 mi) per flight (planned)
Instruments
Dragonfly Mass Spectrometer (DraMS) Dragonfly Gamma-Ray and Neutron Spectrometer (DraGNS) Dragonfly Geophysics and Meteorology Package (DraGMet)
Dragonfly Mission Insignia New Frontiers program ← OSIRIS-REx

Dragonfly is a planned spacecraft and NASA mission, which will send a robotic rotorcraft to the surface of Titan, the largest moon of Saturn. It would be the first aircraft on Titan and is intended to make the first powered and fully controlled atmospheric flight on any moon, with the intention of studying prebiotic chemistry and extraterrestrial habitability. It will then use its vertical takeoffs and landings (VTOL) capability to move between exploration sites.

Titan is unique in having an abundant, complex, and diverse carbon-rich chemistry on the surface of a water-ice-dominated world with an interior water ocean, making it a high-priority target for astrobiology and origin of life studies. The mission was proposed in April 2017 to NASA's New Frontiers program by the Johns Hopkins Applied Physics Laboratory (APL), and was selected as one of two finalists (out of twelve proposals) in December 2017 to further refine the mission's concept. On 27 June 2019, Dragonfly was selected to become the fourth mission in the New Frontiers program.

Overview

Mission concept illustration

Dragonfly is an astrobiology mission to Titan to assess its microbial habitability and study its prebiotic chemistry at various locations. Dragonfly will perform controlled flights and vertical takeoffs and landings between locations. The mission will involve flights to multiple different locations on the surface, which allows sampling of diverse regions and geological contexts.

Titan is a compelling astrobiology target because its surface contains abundant complex carbon-rich chemistry and because both liquid water and liquid hydrocarbons can occur on its surface, possibly forming a prebiotic primordial soup.

A successful flight of Dragonfly will make it the second rotorcraft to fly on a celestial body other than Earth, following the success of a Martian technology demonstration UAV helicopter, Ingenuity, which landed on Mars with the Perseverance rover on 18 February 2021 as part of the Mars 2020 mission and successfully achieved powered flight on 19 April 2021.

History

The previously passed over TSSM mission proposed a Titan aircraft in the form of a Montgolfier balloon with a boat-lander gondola.

The initial Dragonfly conception took place over a dinner conversation between scientists Jason W. Barnes of Department of Physics, University of Idaho, (who had previously made the AVIATR proposal for a Titan aircraft) and Ralph Lorenz of Johns Hopkins University Applied Physics Laboratory, and it took 15 months to make it a detailed mission proposal. The principal investigator is Elizabeth Turtle, a planetary scientist at the Johns Hopkins Applied Physics Laboratory.

The Dragonfly mission builds on several earlier studies of Titan mobile aerial exploration, including the 2007 Titan Explorer Flagship study, which advocated a Montgolfier balloon for regional exploration, and AVIATR, an airplane concept considered for the Discovery program. The concept of a rotorcraft lander that flew on battery power, recharged during the 8-Earth-day Titan night from a radioisotope power source, was proposed by Lorenz in 2000. More recent discussion has included a 2014 Titan rotorcraft study by Larry Matthies, at the Jet Propulsion Laboratory, that would have a small rotorcraft deployed from a lander or a balloon. The hot-air balloon concepts would have used the heat from a radioisotope thermoelectric generator (RTG).

Leveraging proven rotorcraft systems and technologies, Dragonfly will use a multi-rotor vehicle to transport its instrument suite to multiple locations to make measurements of surface composition, atmospheric conditions, and geologic processes.

Dragonfly and CAESAR, a comet sample return mission to 67P/Churyumov–Gerasimenko, were the two finalists for the New Frontiers program Mission 4, and on 27 June 2019, NASA selected Dragonfly for development; it will launch in June 2027.

Funding

The CAESAR and Dragonfly missions received US$4 million funding each through the end of 2018 to further develop and mature their concepts. NASA announced the selection of Dragonfly on 27 June 2019, which will be built and launched by June 2027. Dragonfly will be the fourth in NASA's New Frontiers portfolio, a series of principal investigator-led planetary science investigations that fall under a development cost cap of approximately US$850 million, and including launch services, the total cost will be approximately US$1 billion.

Science objectives

Titan is similar to the very early Earth, and can provide clues to how life may have arisen on Earth. In 2005, the European Space Agency's Huygens lander acquired some atmospheric and surface measurements on Titan, detecting tholins, which are a mix of various types of hydrocarbons (organic compounds) in the atmosphere and on the surface. Because Titan's atmosphere obscures the surface at many wavelengths, the specific compositions of solid hydrocarbon materials on Titan's surface remain essentially unknown. Measuring the compositions of materials in different geologic settings will reveal how far prebiotic chemistry has progressed in environments that provide known key ingredients for life, such as pyrimidines (bases used to encode information in DNA) and amino acids, the building blocks of proteins.

Areas of particular interest are sites where extraterrestrial liquid water in impact melt or potential cryovolcanic flows may have interacted with the abundant organic compounds. Dragonfly will provide the capability to explore diverse locations to characterize the habitability of Titan's environment, investigate how far prebiotic chemistry has progressed, and search for biosignatures indicative of life based on water as solvent and even hypothetical types of biochemistry.

The atmosphere contains plentiful nitrogen and methane, and strong evidence indicates that liquid methane exists on the surface. Evidence also indicates the presence of liquid water and ammonia under the surface, which may be delivered to the surface by cryovolcanic activity.

Design and construction

Titan has a dense atmosphere and low gravity compared to Earth, two factors facilitating propelled flight.

 

The multi-mission radioisotope thermoelectric generator of Mars Science Laboratory, sent to the surface of Mars to power that robotic rover.

Dragonfly will be a rotorcraft lander, much like a large quadcopter with double rotors, an octocopter. Redundant rotor configuration will enable the mission to tolerate the loss of at least one rotor or motor. Each of the craft's eight rotors will be about 1 m (3.3 ft) in diameter. The aircraft will travel at about 10 m/s (36 km/h; 22 mph) and climb to an altitude of up to 4 km (13,000 ft).

Flight on Titan is aerodynamically benign as Titan has low gravity and little wind, and its dense atmosphere allows for efficient rotor propulsion. The radioisotope thermoelectric generator (RTG) power source has been proven in multiple spacecraft, and the extensive use of quad drones on Earth provides a well-understood flight system that is being complemented with algorithms to enable independent actions in real-time. The craft will be designed to operate in a space radiation environment and in temperatures averaging 94 K (−179.2 °C).

Titan's dense atmosphere and low gravity mean that the flight power for a given mass is a factor of about 40 times lower than on Earth. The atmosphere has 1.45 times the pressure and about four times the density of Earth's, and local gravity (13.8% of Earth's) will make it easier to fly, although cold temperatures, lower light levels and higher atmospheric drag on the airframe will be challenges.

Dragonfly will be able to fly several kilometers, powered by a lithium-ion battery, which will be recharged by a Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) during the night. MMRTGs convert the heat from the natural decay of a radioisotope into electricity. The rotorcraft will be able to travel ten kilometers on every battery charge and stay aloft for a half hour each time. The vehicle will use sensors to scout new science targets, and then return to the original site until new landing destinations are approved by mission controllers.

The Dragonfly rotorcraft will be approximately 450 kg (990 lb), and packaged inside a 3.7 m (12 ft) diameter heatshield. Regolith samples will be obtained by two sample acquisition drills and hoses, one on each landing skid, for delivery to the mass spectrometer instrument.

An artist's concept of the Dragonfly rotorcraft-lander approaching a site on Titan.

The craft will remain on the ground during the Titan nights, which last about 8 Earth days or 192 hours. Activities during the night may include sample collection and analysis, seismological studies like diagnosing wave activity on the northern hydrocarbon seas, meteorological monitoring, and local microscopic imaging using LED illuminators as flown on Phoenix lander and Curiosity rover. The craft will communicate directly to Earth with a high-gain antenna.

The Penn State Vertical Lift Research Center of Excellence is responsible for rotor design and analysis, rotorcraft flight-control development, scaled rotorcraft testbed development, ground testing support, and flight performance assessment.

Scientific payload

• DraMS (Dragonfly Mass Spectrometer) is a mass spectrometer to identify chemical components, especially those relevant to biological processes, in surface and atmospheric samples.
• DraGNS (Dragonfly Gamma-Ray and Neutron Spectrometer), consists of a deuterium-tritium Pulsed Neutron Generator and a set of a gamma-ray spectrometer and neutron spectrometer to identify the surface composition under the lander.
• DraGMet (Dragonfly Geophysics and Meteorology Package) is a suite of meteorological sensors including a seismometer.
• DragonCam (Dragonfly Camera Suite) is a set of microscopic and panoramic cameras to image Titan's terrain and scout for scientifically interesting landing sites.
• In addition, Dragonfly will use multiple engineering and monitoring instruments to determine characteristics of Titan's interior and atmosphere.

Trajectory

Dragonfly is expected to launch in June 2027, and will take seven years to reach Titan, arriving by 2034. The spacecraft will perform a gravitational assist flyby of Venus, and three passes by Earth to gain additional velocity. The spacecraft will be the first dedicated outer solar system mission to not visit Jupiter as it will not be within the flight path at the time of launch.

Entry and descent

The cruise stage will separate from the entry capsule ten minutes before encountering Titan's atmosphere. The lander will descend to the surface of Titan using an aeroshell and a series of two parachutes, while the spent cruise stage will burn up in uncontrolled atmospheric entry. The duration of the descent phase is expected to be 105 minutes. The aeroshell is derived from the Genesis sample return capsule, and the PICA heat shield is similar to MSL and Mars 2020 design and will protect the spacecraft for the first 6 minutes of its descent.

At a speed of Mach 1.5, a drogue parachute will deploy, to slow the capsule to subsonic speeds. Due to Titan's comparably thick atmosphere and low gravity, the drogue chute phase will last for 80 minutes. A larger main parachute will replace the drogue chute when the descent speed is sufficiently low. During the 20 minutes on the main chute, the lander will be prepared for separation. The heat shield will be jettisoned, the landing skids will be extended, and sensors such as radar and lidar will be activated. At an altitude of 1.2 km (0.75 mi), the lander will be released from its parachute, for a powered flight to the surface. The specific landing site and flight operation will be performed autonomously. This is required since the high gain antenna will not be deployed during descent, and because communication between Earth and Titan takes 70–90 minutes, each way.

Landing site

Shangri-La is the large, dark region at the center of this infrared image of Titan.

 

The Selk impact crater on Titan, as imaged by the Cassini orbiter's radar, is 90 km (56 mi) in diameter.

The Dragonfly rotorcraft will land initially in dunes to the southeast of the Selk impact structure at the edge of the dark region called Shangri-La. It will explore this region in a series of flights of up to 8 km (5.0 mi) each, and acquire samples from compelling areas with a diverse geography. After landing it will travel to the Selk impact crater, where in addition to tholin organic compounds, there is evidence of past liquid water.

The Selk crater is a geologically young impact crater 90 km (56 mi) in diameter, located about 800 km (500 mi) north-northwest of the Huygens lander. (7.0°N 199.0°W) Infrared measurements and other spectra by the Cassini orbiter show that the adjacent terrain exhibits a brightness suggestive of differences in thermal structure or composition, possibly caused by cryovolcanism generated by the impact — a fluidized ejecta blanket and fluid flows, now water ice. Such a region featuring a mix of organic compounds and water ice is a compelling target to assess how far the prebiotic chemistry may have progressed at the surface.