NASA studying larger Mars helicopters

With the Ingenuity helicopter continuing to demonstrate its abilities on Mars, NASA engineers are examining concepts for larger, more capable rotorcraft that could be flown on future missions. Ingenuity performed its eighth flight on Mars June 21, traveling 160 meters and landing at a new site 133.5 meters from the Perseverance rover. The flight, which lasted 77.4 seconds, was the third since Ingenuity shifted from its original five-flight technology demonstration mission, proving it could fly in the thin Martian atmosphere, to serving as an operations demonstration working in conjunction with Perseverance. Those flights are scheduled to continue for at least a few more months. “Part of what is going to be happening in the coming months are additional flights that demonstrate how this dance can work between the helicopter and the rover,” said Ken Farley, chief scientist for the Mars 2020 mission, during a June 21 meeting of NASA’s Mars Exploration Program Analysis Group (MEPAG). That includes, he said, obtaining imagery of places that the rover cannot travel, such as a region called Seitah that is too rough for the rover to traverse. Helicopter images could also be used to create “terrain meshes” to enable longer drives by the rover by giving it information about terrain the rover’s own cameras, mounted on a mast, cannot see.

A concept called Mars Science Helicopter, shown in a video at a recent Mars exploration meeting, would fly a 30-kilogram hexacopter capable of traveling up to 10 kilometers per flight and carry five kilograms of science payloads. Credit: NASA JPL/NASA Ames/AeroVironment

“That is going to continue for at least few more months, with a cadence of a couple of flights,” he said. “That is the level that we can easily make this coordination work.”

“We hope to fly many, many more,” said Teddy Tzanetos of the Jet Propulsion Laboratory, part of the Ingenuity team, at MEPAG. The helicopter has flown a cumulative distance of nearly one kilometer, including 266 meters in one flight. However, the project is considering “stretch capabilities” of individual flights up to one kilometer long, lasting up to three minutes. “That would really be pushing the limit of what the technology demonstrator is capable of.”

Data collected by Ingenuity is supporting planning of a future helicopter design by engineers at JPL, NASA’s Ames Research Center and AeroVironment. The Mars Science Helicopter would be a hexacopter, or six-rotor helicopter, with a mass of about 30 kilograms. Ingenuity, by contrast, weighs 1.8 kilograms. Mars Science Helicopter could carry as much as five kilograms of science payloads and fly up to 10 kilometers per sortie.

“We’re trying to look at the science applications: what science is enabled by having the aerial dimension added,” he said. That includes traveling to locations inaccessible to rovers, such as the sides of cliffs and into caves.

In a white paper submitted as part of the ongoing planetary science decadal survey, scientists identified several applications for the Mars Science Helicopter, from studies of Martian geology and atmosphere to examination of “special regions” of astrobiological interest without risk of contamination.

One notional mission described in the paper is to visit an outflow channel called Mawrth Vallis that is difficult for rovers to access, collect samples at several locations and then return them to a lander for analysis. “We’re open to ideas and new concepts,” Tzanetos said.

He did not discuss potential costs or flight opportunities for Mars Science Helicopter, although the white paper notes that “there are viable roles for [Mars Science Helicopter] across a range of mission classes,” including NASA’s Discovery and New Frontiers classes. A simpler helicopter design included in the white paper, essentially a scaled-up version of Ingenuity, “is sufficiently low mass and low volume that it should be considered in all future launch opportunities to Mars’ surface,” the paper concluded.

Agency officials said earlier this year they were not considering adding a helicopter to its next lander mission, the Sample Return Lander that is part of the Mars Sample Return program and is scheduled for launch no earlier than 2026.

Ligado Networks passes 3GPP review for 5G plan

Ligado Networks is a step closer toward using its L-band satellite spectrum for terrestrial wireless services in the U.S., after getting clearance from the 3GPP consortium that sets global communications standards for 5G. The company said June 21 that 3GPP approved technical specifications that enable vendors to build 5G-compatible products on its spectrum. It comes after the Federal Communications Commission granted Ligado a modification to its L-band license in April 2020, despite opposition from the Pentagon and other government agencies over GPS interference concerns. The FCC unanimously approved Ligado’s plan to use L-band for a 5G network, following a four-year proceeding, with conditions including reduced power limits and a requirement that part of it be used as a “guard band” near adjacent operations such as GPS. In October, Ligado said it had raised nearly $4 billion in new capital to develop a private network solution for energy, manufacturing, health care, transportation and other infrastructure sectors. “The final major step for Ligado will involve getting chipset and radio vendors to incorporate the L-Band into their designs, paving the way for a carrier to deploy the L-Band on towers and small cells and to sell devices that contain L-Band-supporting chipsets,” New Street Research analyst Jonathan Chaplin wrote in a report to investors. “This final leg of the process is likely to take some time, but could be accelerated by the support of a large industry player (one of the carriers), who can more easily encourage their vendors to integrate the spectrum into their equipment.”

Ligado announced an agreement June 22 with Nokia to develop 5G base station radios that will be compatible with its spectrum in North America.

“Our partnership with an industry leader like Nokia is a significant milestone for our company and brings the deployment of L-Band spectrum in 5G mobile networks one step closer to reality,” Ligado chief technology officer Maqbool Aliani said in a statement.

“Nokia is a key partner in Ligado’s commercial efforts to develop the vendor ecosystem around this lower mid-band spectrum, and we look forward to advancing our collaboration activities to ready the L-Band for 5G network deployments.”

Ligado is also collaborating with Japan-based network operator Rakuten Mobile on its private network plans, aiming to deploy field trials over the next 12 months.

U.S.-based satellite operator Globalstar achieved 3GPP approval in March 2020 amid global ambitions to use some of its S-band spectrum for terrestrial wireless services.

Announcing financial results May 6, 2021, Globalstar executive chair Jay Monroe said the company was reviewing “several private networking opportunities of varying sizes” for the frequencies.

“We will soon be at the point where the only impediment to terrestrial deployments will be commercial negotiations,” Monroe said.

A New Era of Spaceflight? Exciting Advances in Rocket Propulsion

The US Defense Advanced Research Projects Agency (Darpa) has recently commissioned three private companies, Blue Origin, Lockheed Martin and General Atomics, to develop nuclear fission thermal rockets for use in lunar orbit. Such a development, if flown, could usher in a new era of spaceflight. That said, it is only one of several exciting avenues in rocket propulsion. Here are some others. The standard means of propulsion for spacecraft uses chemical rockets. There are two main types: solid-fueled (such as the solid rocket boosters on the Space Shuttle), and liquid-fueled (such as the Saturn V). In both cases, a chemical reaction is employed to produce a very hot, highly pressurized gas inside a combustion chamber. The engine nozzle provides the only outlet for this gas which consequently expands out of it, providing thrust. The chemical reaction requires a fuel, such as liquid hydrogen or powdered aluminum, and an oxidizer (an agent that produces chemical reactions) such as oxygen. There are many other variables which ultimately also determine the efficiency of a rocket engine, and scientists and engineers are always looking to get more thrust and fuel efficiency out of a given design.

Recently, private company SpaceX has been conducting test flights of their Starship launcher prototype. This vehicle uses a “full-flow staged combustion (FFSC) engine,” the Raptor, which burns methane for fuel and oxygen for oxidizer. Such designs were tested by the Russians in the 1960s and the US government in the 2000s, but as yet none has flown in space. The engines are much more fuel-efficient and can generate a much higher thrust-to-weight ratio than traditional designs.
Fission thermal rockets

The nucleus of an atom consists of sub-atomic particles called protons and neutrons. These determine the mass of an element – the more protons and neutrons, the heavier it is. Some atomic nuclei are unstable and can be split into several smaller nuclei when bombarded with neutrons. This is the process of nuclear fission, and it can release an enormous amount of energy. As the nuclei decay, they also release more neutrons which go on to fissure more atoms – producing a chain reaction.

In a nuclear fission thermal rocket, a propellant gas, such as hydrogen, is heated by nuclear fission to high temperatures, creating a high-pressure gas within the reactor chamber. Like with chemical rockets, this can only escape via the rocket nozzle, again producing thrust. Nuclear fission rockets are not envisaged to produce the kind of thrust necessary to lift large payloads from the surface of the Earth into space. Once in space though, they are much more efficient than chemical rockets – for a given mass of propellant, they can accelerate a spacecraft to much higher speeds.

Nuclear rocket engine being transported to test stand in Jackass Flats, Nevada, in 1967. Credit: AEC-NASA

Nuclear fission rockets have never been flown in space, but they have been tested on the ground. They should be able to shorten flight times between Earth and Mars from some seven months to about three months for future crewed missions. Obvious drawbacks, however, include the production of radioactive waste, and the possibility of a launch failure which could result in radioactive material being spread over a wide area.

A major engineering challenge is to sufficiently miniaturise a reactor so that it will fit on a spacecraft. There is already a burgeoning industry in the production of compact fission reactors, including the development of a fission reactor which is smaller than an adult human.

Electric propulsion

A staple of science fiction, real ion drives generate charged particles (ionization), accelerate them using electric fields and then fire them from a thruster. The propellant is a gas such as xenon, a fairly heavy element that can be easily electrically charged.

Ion thruster of NASA’s Deep Space 1. Credit: NASA

As the charged xenon atoms accelerate out of the thruster, they transfer a very small amount of momentum (the product of mass and velocity) to the spacecraft, providing gentle thrust. While slow, ion drives are among the most fuel-efficient of all spacecraft propulsion methods, so could get us further. Ion drives are commonly used for attitude control (changing which direction a spacecraft is facing) and have been considered for deorbiting old satellites.

Current ion engines are powered by solar cells, effectively making them solar powered, and requiring very little propellant. They have been used on ESA’s SMART-1 mission to the Moon and Bepi-Colombo mission en-route to Mercury. NASA is currently developing a high-power electric propulsion system for the Lunar Gateway, an outpost that will orbit the Moon.

Solar sails

While propulsion usually requires propellant of some description, a more “green” method relying only on light from the Sun itself

                                                     Ikaros solar sail. Credit: Pavel Hrdlička CC BY-SA

Sails rely on the physical property of conservation of momentum. On Earth, we are used to seeing this momentum as a dynamic pressure from air particles blowing into a sheet when sailing, propelling a vessel forwards. Light is comprised of photons, which have no mass, but they do have momentum and can transfer it to a sail. As the energies of individual photons are very small, an extremely large sail size is needed for any appreciable acceleration.

The speed gain will also depend on how far from the Sun you are. At Earth, the power received from sunlight is about 1.3 kW per square meter. If we had a sail the size of a football pitch, this would equate to 9.3 MW, providing a very low acceleration, even to a low mass object.

Solar sails have been tested by the Japanese IKAROS spacecraft which successfully flew by Venus, and the Planetary Society Lightsail-2, which is presently in orbit around Earth.

A way of improving efficiency and reducing sail size is to use a laser to propel the spacecraft forward. Lasers produce very intense beams of photons which can be directed onto a sail to provide much higher acceleration, but would require being built in Earth orbit to avoid loss of intensity in the atmosphere. Lasers have also been proposed as a means of de-orbiting space junk – the light from the laser can slow down a piece of orbital junk, which would then fall out of orbit and burn up in the atmosphere.

The development of nuclear fission rockets may excite some and concern others. However, as private companies and national space agencies are increasingly committing to a sustained human presence in space, these alternative means of propulsion will become more mainstream and have the potential to revolutionize our nascent space-faring civilization.

Astra to acquire spacecraft propulsion company Apollo Fusion

Launch vehicle developer Astra is acquiring Apollo Fusion, a company developing electric propulsion systems for spacecraft, as part of its effort to create vertically integrated space systems. Astra is purchasing Apollo Fusion for $30 million in stock and $20 million in cash in a deal announced June 7. The deal includes an additional $95 million in earn-out incentives if Apollo Fusion reaches certain technical and revenue milestones. Astra will incorporate Apollo Fusion’s Apollo Constellation Engine electric propulsion systems in satellite buses the company is developing to provide an integrated solution to customers. Astra revealed its satellite plans in February when it announced it would merge with a special purpose acquisition company (SPAC), Holicity. The companies said the acquisition will close after Astra completes its merger with Holicity later this year. In an interview, Chris Kemp, chief executive of Astra, said that Apollo Fusion’s thrusters fill a technology gap for those future satellites. “What this is about is adding a really core piece of technology to Astra’s platform,” he said. “It’ll unlock a whole new set of customer opportunities for us.” “The next puzzle piece is the vertically integrated spacecraft. So, as we started to look at that, what are the core technologies that drive that?” he said. “This engine is one of those key cornerstones of that space platform we’re building.” Mike Cassidy, chief executive of Apollo Fusion, said customers of both his company’s thrusters and Astra’s rockets were looking for an integrated solution. “A lot of our customers were asking us for the total solution for getting from the ground from the orbit they want to go, and Chris’s customers are asking the same thing,” he said in an interview.

Apollo Fusion's electric thrusters will be integrated into satellite systems being developed by Astra, but will also continue to be sold to other customers. Credit: Apollo Fusion

Apollo Fusion, which has sold its Apollo Constellation Engine to several customers, most recently York Space Systems, will continue to market the thruster to other companies. “We are financially motivated to do that part of the deal, and Astra has made very good incentives for us to keep doing that,” Cassidy said.

“Mike has an incredible customer manifest and pipeline, and we want to continue to serve those customers,” Kemp said of Apollo Fusion. “We’re incorporating what they’re [Apollo Fusion] doing into our product as quickly as we can.”

Both companies have emphasized plans for mass production of their systems. Astra has a goal of performing daily launches as soon as the middle of the decade, while Apollo Fusion has emphasized production partnerships that would allow it to manufacture its thrusters in large quantities.

Cassidy said he expects to leverage Astra’s projected launch cadence to speed up development and testing of new thrusters. “The way it is now, we have to wait 9 or 12 months to do a test launch,” he said. “But in the future, we’ll be able to do a test launch in two or four months.”

Kemp said he saw a lot of similarities between the two companies, and having known Cassidy for several years, it was clear that a deal made sense. “It’s really like we’re sister companies and their technology was just a big missing piece of our overall platform,” he said.

Astra roadmap

Astra’s acquisition of Apollo Fusion is the latest in a series of developments for the company. It announced May 18 a contract with Planet to perform multiple launches of Planet’s imaging satellites in 2022.

Kemp said in the interview that Astra has more than 50 launches under contract, serving a mix of government and commercial customers, although Planet is the first customer it’s publicly announced. “Planet is probably the pioneer in the small satellite space,” he said. “We couldn’t be more proud to have them as the first customer we could announce.”

Astra also disclosed that it has a roadmap to develop larger vehicles, with the goal of placing up to 500 kilograms into orbit. The company did not disclose technical details of that roadmap, or a schedule for producing those larger vehicles.

Kemp said plans for various megaconstellations influenced that roadmap. “We want to converge with what these megaconstellation operators are designing and flying in 2023,” he said. “It’s about being the most responsive launch service provider and also being the best way for us to build our own platform.”

He described an iterative process for gradually scaling up the company’s launch vehicles to achieve that 500-kilogram target. “My goal is to have as many iterations as possible, where the engineers can add these things incrementally,” he said, gradually increasing performance instead of making a big jump from 50 to 500 kilograms.

Up next for Astra is beginning commercial launches. Kemp said the company’s next launch, after a December 2020 flight that nearly reached orbit, is scheduled for this summer. Astra expects to begin monthly launches in the fourth quarter.

NASA selects two Venus missions for Discovery program

For the first time in more than three decades, NASA has announced it will send a robotic mission to Venus, selecting two proposals in the latest round of its Discovery program. NASA Administrator Bill Nelson announced at the end of a “State of NASA” speech at NASA Headquarters June 2 that the DAVINCI+ and VERITAS missions will launch to Venus in the late 2020s, having beat out competing proposals for missions to Jupiter’s volcanic moon Io and Neptune’s large moon Triton that were also selected as finalists in early 2020. “These two sister missions both aim to understand how Venus became an inferno-like world capable of melting lead at the surface,” Nelson said. “They will offer the entire science community the chance to investigate a planet we haven’t been to in more than 30 years.” DAVINCI+, or Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging, will send a probe into the planet’s atmosphere, measuring noble gases and other elements that can provide information on how its runaway greenhouse effect developed. Cameras on the descent probe will provide high-resolution images of geological features known as “tesserae” that may be similar to Earth’s continents. VERITAS, or Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy, will map the planet from orbit using a synthetic aperture radar system. It will also search for infrared emissions that could help scientists determine if there is active volcanism.

“It is astounding how little we know about Venus, but the combined results of these missions will tell us about the planet from the clouds in its sky through the volcanoes on its surface all the way down to its very core,” said Tom Wagner, NASA’s Discovery program scientist, in a statement. “It will be as if we have rediscovered the planet.”

DAVINCI+ will be led by NASA’s Goddard Space Flight Center, while VERITAS will be run by the Jet Propulsion Laboratory. Lockheed Martin will build the spacecraft for both missions.

Each mission has an estimated cost of $500 million, with launches expected between 2028 and 2030. Launch contracts will be awarded later in each mission’s development.

In a briefing with reporters after the State of NASA speech, Thomas Zurbuchen, NASA associate administrator for science, said all four proposals, including the Io Volcano Observer and Trident mission to Triton, rated well. “This is not the case where one of these missions had a massively bigger risk. It’s not the case that one of them was ground-ruled out in some way,” he said.

While both DAVINCI+ and VERITAS are going to Venus, he noted that the two missions are “massively different” in their science, one focusing on the atmosphere and the other the surface. “In the end, those two swung, in terms of science return and programmatic match, to the top,” he said. “Those were the best missions, and that’s why we selected them.”

The two winning missions are updated versions of proposals that were finalists in the previous round of the Discovery program. NASA instead selected two asteroid missions, Lucy and Psyche, in early 2017.

Having been through the competition before helped DAVINCI+ and VERITAS. “I hardly recognized the proposal,” he said of VERITAS in particular. “The science was just so much better. The ratings were so much better than the previous round.”

Both missions will host technology demonstrations in addition to their primary science payloads. VERITAS will host an updated version of a deep space atomic clock first flown on an Earth-orbiting spacecraft in 2019 that will assist in radio science observations and autonomous spacecraft maneuvers. DAVINCI+ will fly a new ultraviolet imaging spectrometer.

The missions will be the first NASA missions dedicated to Venus since the Magellan radar mapper orbiter, launched in 1989. Magellan’s mission ended in 1994, and while scientists have been able to participate in European and Japanese Venus orbiter missions, or take advantage of limited observations by other spacecraft flying by Venus, many researchers had been advocating for years for a new Venus mission.

“In the science community, I can tell you, this is resonating,” Nelson said in the post-speech briefing. “They’re excited about this.”

Other countries and even private ventures are planning missions to Venus. Russia has been working for several years on a mission concept called Venera-D that includes an orbiter and lander, which could feature some NASA participation. India is developing a Venus orbiter mission called Shukrayaan scheduled for launch in 2024. The European Space Agency is considering a Venus orbiter called EnVision for its next medium-class mission.

Perhaps most intriguingly, Rocket Lab, the small launch vehicle and smallsat developer, has been leading efforts to send a small mission to Venus. That mission has been motivated in part by the potential discovery of phosphine in the planet’s atmosphere, a gas that could be evidence of life. Scientists announced in September 2020 the potential detection of phosphine based on analysis of ground-based infrared and microwave observations, but other scientists have questioned that detection.

Peter Beck, Rocket Lab’s chief executive, has said on numerous occasions that the company is working on a smallsat mission that would plunge into the atmosphere to search for phosphine or other biosignatures. That could launch as soon as 2023, although the company has provided few details about the mission’s development.

“Venus is the most underrated planet in our solar system,” he said during a May 27 webinar by Bessemer Venture Partners, citing the potential lessons from that planet’s runaway greenhouse that could apply to Earth. “I think we can learn a tremendous amount, scientifically, from Venus.”