Tag: Spaceflight

In my previous Space Sunday, I covered some of the renewed interest in nuclear propulsion for space missions – and it certainly is a hot topic (no pun intended). Just 24 hours after that article was published, NASA and the US Defense Advanced Research Projects Agency (DARPA) announced they had signed an interagency agreement to develop a nuclear-thermal propulsion (NTP) concept.

Referred to as the Demonstration Rocket for Agile Cislunar Operations (DRACO), the three-phase programme will look to develop and enhance an NTP propulsion system capable of operating between Earth and the Moon and eventually Earth and Mars, potentially enabling fast transit times to the latter measured in weeks rather than months. Nor is this simply a computer modelling exercise: the agencies plan to fly a demonstrator of the propulsion unit in early 2027.

As I noted in my previous piece, NTP uses a nuclear reactor to heat liquid hydrogen (LH2) propellant, turning it into ionized hydrogen gas (plasma) channelled through engine bells similar to those seen in chemical rockets to generate thrust. As I also noted, NTP for space vehicle propulsion is not new; both the US and the former Soviet Union both pursued NTP projects in the early days of the space race – most notably for the US with the Nuclear Engine for Rocket Vehicle Application (NERVA) project, successfully tested on the ground in 1963/64.

Per the agreement, NASA’s Space Technology Mission Directorate (STMD) will lead the technical development of the nuclear thermal engine, which will be integrated into a vehicle built by DARPA, with that agency leading the overall programme as the contracting authority. Both agencies will collaborate on the overall design of the engine.

DARPA and NASA have a long history of fruitful collaboration in advancing technologies for our respective goals, from the Saturn V rocket that took humans to the Moon for the first time to robotic servicing and refuelling of satellites. The space domain is critical to modern commerce, scientific discovery, and national security. The ability to accomplish leap-ahead advances in space technology through the DRACO nuclear thermal rocket program will be essential for more efficiently and quickly transporting material to the Moon and eventually, people to Mars.

– DARPA director Dr. Stefanie Tompkins

Meanwhile, on January 27th, 2023, the UK’s famed Rolls Royce teased details of its own foray into the space-based nuclear power / propulsion systems: the micro-nuclear reactor (MNR), an extremely robust, self-contained nuclear fission plant which could be used to supply power to bases on the Moon or Mars, or used as a core element in vehicle propulsion systems either individually or as multiple units to provide both thrust and system redundancy, if required.

Development of the MNR started as a result of a 2021 agreement between the United Kingdom Space Agency (UKSA) and Rolls Royce (RR) to study future nuclear power options in space exploration. However, the design for the unit builds on RR’s decades-long expertise in developing power plants for the Royal Navy’s nuclear submarine squadrons and, more particularly a project the company has been developing since 2015 to develop and build small modular reactor (SNRs) to meet the UK’s energy needs (SNRs are self-contained, less complex and lower cost alternative to current nuclear reactors).

Precise details of the size of the unit and its output have not been revealed, although images released by RR suggest a single MNR is around 3 metres in length. In discussing the system, the company indicated its designs have reached a point where it plans to have a full-scale demonstrator / prototype running by 2028.

The MNR forms a part of a broader space strategy from Rolls Royce, which also includes systems for high Mach propulsion systems (e.g. ramjets) which could be combined with rocket propulsion to reach orbit, and a new generation of radioisotope thermal generators (RTGs) for power generation on robotic explorer craft and surface system on the Moon and Mars. The overall aim of the strategy is to offer space agencies and the private sector the ability to easily integrate selected elements of RR’s product offerings into their space projects and programmes.

Returning to NASA, as well as considering the nuclear option, the US agency has been researching the next generation of rocket engines – the rotating detonation rocket engine (RDRE) – and on January 24th, carried out a series of sustained ground tests of a prototype unit.

In a conventional rocket motor, fuel is expended by deflagration combustion – fuel and oxidiser are burnt to produce an energetic gas flow which is then directed through exhaust bells to generate subsonic thrust. With rotating detonation, fuel and oxidiser are injected into a circular channel (annulus). An igniter within the annulus then detonates the initial incoming mix, generating a shockwave which travels around the channel, returning to the point of injection.

At this point, more fuel is injected into the channel to be detonated by the existing shockwave. This increases the shockwave’s speed and force, and the cycle repeats over and over, the shockwave accelerating to supersonic speed, generating high pressures which can be constantly be directed out of the channel to form thrust through an exhaust system even as the shockwave maintains its momentum within the channel.

Whilst this may sound complicated, the upshot is that rotating detonation engines (RDREs) theoretically generate around 25% more thrust than conventional rocket motors, which directly translates to greater delta-V being imparted to vehicles departing Earth, so reducing flight times to the Moon and Mars and elsewhere in the solar system. RDEs could also be inherently less complex than subsonic brethren, reducing the mass of a launch vehicle’s propulsion system.

However, there are drawbacks; for example, the very nature of containing the growing force of the shockwave puts an RDRE under tremendous stress and they have been known to explode. They are also incredibly noisy when built at scale.

Both Russia and Japan have experimented with RDRE technology; in 2018, former Roscosmos chief Dmitry Rogozin claimed Russia had successfully developed the first phase of a 2-tonne class of liquid-fuelled RDRE, although this has yet to be substantiated. In 2021, Japan successfully tested a small-scale (112.4 lbf) RDRE in space, using it to propel the upper stage of a sounding rocket.

The NASA test, carried out at the Marshall Space Flight Centre, Alabama, is the first verified test of a full-scale RDRE. The demonstrator motor operated for a total of 10 minutes, reaching peak thrusts of some 4,000 lbf. This is fairly lightweight by rocket standards, but the aim of the test was not just to generate thrust, but to test the engine’s ability to withstand multiple firings and confirm that a copper alloy referred to as GRCop-42 developed by NASA specifically for use in RDRE engines, was up to the task of reducing the stress on the motor by more efficiently carrying the heat generated by the shockwave away from the annulus structure.

While tests with this motor will continue, NASA is now also moving to the construction of a large unit capable of a sustained 10,000 lbf – the same as mid-range rocket motors – to better understand the potential for RDREs to out-perform “traditional” rocket motors. If successful, it could pave the way for RDRE motors capable of match the output of large-scale engines like the RS-25 used by the Space Launch System (SLS) rocket (418,000 lbf).

Continue reading “Space Sunday: propulsion, planets and pictures” →

Since its launch in April 2018, TESS, the Transiting Exoplanet Survey Satellite, has located 5,969 candidate exoplanets within the immediate (cosmically speaking) neighbourhood of our solar system. Of these, 268 have been confirmed as actual planets – although 1,720 have been dismissed as false positives.

Three of the positives were located orbiting a red dwarf star called TOI 700, some 100 light-years away and within the constellation Dorado, one of which sits within the star’s habitable zone where liquid water might exist on the surface.

And now a fourth has been added to the tally, with the confirmed discovery of TOI 700-e, another planet within the star’s habitable zone. Like TOI 700-d, the other planet within the star’s habitable zone, it is roughly Earth-sized – around 95% the size of Earth, marking it as slightly smaller than TOI 700-d, which is 1.1 times the side of Earth.

This is one of only a few systems with multiple, small, habitable-zone planets that we know of. That makes the TOI 700 system an exciting prospect for additional follow-up. Planet e is about 10% smaller than planet d, so the system also shows how additional TESS observations help us find smaller and smaller worlds.

– Emily Gilbert, NASA’s Jet Propulsion Laboratory

TOI 700-d was actually the first Earth-sized planet TESS located within the habitable zone of s star, and wobbles in its orbit, and those of the other two planets TOI 700-b and TOI 700-c, led Gilbert and her team to task TESS with a re-visit to the system in the belief another planet might be hidden within it, hence the discovery of TOI 700-e.

All of the planets are likely tidally locked to their star – always keeping the same side facing it as they make their orbits. This makes the chances of them supporting life complicated, as one side is always exposed to the heat of the star, and the other to the freezing cold of space. Between them, along the terminator, they may have more temperate regions, but assuming the planets have an atmosphere, the temperate regions could be ravaged by storms where warm and cold fronts continuous meet.  All four planets have short orbital periods – 10 days for the innermost planet 700-b to just over 37 days for the newly-discovered 700-e. Planets b, d, and e are likely rocky, while planet c is likely more similar to Neptune.

The term habitable zone also deserves some expansion, as it actually covers two overlapping zones around a star, the optimistic habitable zone (OHZ) and the conservative habitable zone (CHZ). The former is a region around a star where water may have existed at some point in the planet’s history; the CHZ is a more tightly-constrained region where scientists hypothesize liquid surface water might have existed for most of a planet’s history and it may have developed a more Earth-like atmosphere. TOI 700-e is in the optimistic habitable zone for its star.

That said, determining the habitability of solid rocky planets within the OHZ / CHZ of a star is impossible at our stage of exoplanet science. Simply put, they are fat too small to be seen well enough to make firm conclusions. All scientists can say is that a planet might be potentially habitable and then explain their detailed findings. In the case of TOI 700-e, the science team notes:

With a radius of 0.953 Earth radii, TOI-700-e is likely a rocky planet with a probability of 87%, [and a] timescale for tidal locking of to be on order a few million years. Given the age of the system, it is likely that the planet is in a locked-in synchronous or pseudo-synchronous rotation.

– Emily Gilbert, NASA’s Jet Propulsion Laboratory

One interesting aspect of the TOI 700 system is that while the star in an M-type red dwarf, a spectral type known for violent, powerful flares which could play havoc with the atmosphere and environment of the planets orbiting it. However, TOI 700 is older and more quiescent than its siblings and so perhaps less violent towards its children. Given this, and the fact it is a multi-planet system with two Earth-sized planets sitting within it OHZ, it forms a counterpoint to TRAPPIST-1, a younger, more aggressive M-class star with seven Earth-sized planets orbiting them, four of them within its own OHZ. Studies of both systems offers the potential for extended comparative study, potentially helping scientists better understanding of exoplanet systems form and M-type stars (the most numerous type of star in the galaxy), and how the planets within them retain (or lose) their atmospheres.

The discovery of TOI 700-e is a further demonstration on how the search for exoplanets is progressing. Prior to the launch of the long-running Kepler Space Telescope, only a handful of exoplanets had been discovered, and the number is now over 5,000, with discoveries in recent years revealing more and more Earth-sized worlds and multi-planet systems.

While the number of confirmed planets is small, TESS is adding to that total, and out ability to understand such worlds is gaining a boost thanks the James Webb Space Telescope (JWST). The instruments on the telescope are designed to study exoplanet atmospheres and use spectroscopy to determine their compositions. In fact, this work has already started with the planet Bocaprins (WASP 39b), a “hot Jupiter” planet 700 light years way, with JWST confirming its atmosphere contains sodium, potassium, carbon dioxide, carbon monoxide, water vapour and most significantly, sulphur dioxide.

The last is important both because it is the first time scientists have found this molecule anywhere outside of our Solar System, confirming photochemical reactions can take place in the atmospheres of exoplanets, and confirms JWST can detect such photochemical reactions within planetary atmospheres over vast distances – .something which could be an important factor in determining what interactions might be taking place in the atmospheres of many exoplanets.

As such, exoplanet science is maturing rapidly.

Soyuz MS-22 Update

Russia has confirmed it will launch Soyuz MS-23 to the International Space Station in an uncrewed mode to replace the Soyuz MS-22 vehicle which suffered a major coolant leak in December 2022, following what is theorised a piece of dust striking the external radiator at a speed of 7 km/s.

Following the accident, a number of western experts suggested the Soyuz vehicle would be incapable of maintaining a safe temperature in the crew cabin during a return to Earth. After a month-long review of the situation, including examining options for a space-based repair, the Russian space agency Roscosmos has reached the same conclusion.

Soyuz MS-23 will therefore launch on or around February 20th in an automated configuration to provide the means for cosmonauts Sergey Prokopyev and Dmitri Petelin and NASA astronaut Franco Rubio to return to Earth at a later date – exactly when that will be is unclear; as a result of needing to use MS-23 as a replacement vehicle, crew rotations on the Russian side of things will be disrupted, and so Roscomos expects the MS-22 crew to extend their stay on the station by “several months”.

However, the February launch for MS-23 still means that should an emergency evacuation of the station be required in the next month, the crew of MS-22 would be without a ride home. To cover this, it has been suggested at least one MS-22 crew member (likely Rubio) could return on Crew Dragon 5 with the four astronauts it flew to the ISS in October 2022, and remaining MS-22use that vehicle -the thinking at Roscosmos being that with a smaller crew, the damaged cooling system on the Soyuz wouldn’t be so strained and could maintain “safe” temperatures within the vehicle.

Once MS-23 has docked at the station, MS-22 will be prepared for an automated return to Earth, where the investigation into the coolant loss will continue.

Repairs to the damaged vehicle were ruled out due to the difficulties involved in any spacewalk to do so – not the least of which was the risk of ammonia contaminating the spacesuits used and then being brought back into the ISS in high enough concentrations that it might pose a serious health risk if inhaled by any of the crew.

Continue reading “Space Sunday: Exoplanets and updates” →

China continues to grow and expand its astronomy and space aspirations. In a series of announcements, the country has indicated its aims for Earth-based astronomy, the expansion of its space station, international co-operation and more on it plans for a presence on the Moon.

With the Tiangong station only having recently been “completed” in terms of its pressurised modules with the arrival of the Mengtian science module in October, China had originally indicated that the only remaining module awaiting delivery to the station was the Xuntian space telescope, capable of docking with the station for maintenance, but designed to operate as a free-flying automated platform to be launched in 2023.

However, Wang Xiang, director of space station systems at the China Academy of Space Technology (CAST), has indicated China is considering adding a second “core” module to Tiangong. If this goes ahead, it will be mated to the axial port of the current docking hub at the forward end of the Tinahe-1 module.

According to Wang, the new module will provide a larger and more comfortable living environment for crews, and would include its own docking hub capable of supporting two further modules as well as accepting vehicles docking at its the axial port. This would allow the station to double in size and support larger crew numbers, as well as allowing it to operate for considerably longer than the planned 10-year time frame.

In addition, CAST has announced China is working with Saudi Arabia, the United Arab Emirates and other Gulf states to reach partnership agreements which could see these states working alongside China aboard Tiangong, developing a human presence on the Moon and in deep-space astronomy and robotic exploration.

Among other aspects of the agreement is the potential to establish a China-GCC (Gulf Cooperating Council – comprising Saudi Arabia, Qatar, UAE, Bahrain, Oman, and Kuwait) joint centre for lunar exploration, which would also oversee the selection and training of tiakonauts from GCC member states.

In terms of the latter, China is keen to gain international partners in its vision for lunar exploration in order to match the Artemis Accords. The latter is a set of a non-binding agreements that (to date) has seen 23 nations agree to support the US-led return to the Moon with personnel, materiel and scientific endeavours.

China’s lunar aspirations are seen by some as potentially kicking-off a new “space race”, given both it and the United States have identified the Moon’s south polar regions as the most likely location for establishing bases, given the relative accessibility of water ice within craters there. Whether this proves to be the case remains to be seen; certainly, there is a degree of chaffing within China at being excluded from all international space efforts involving the United States; however, the country has been developing its own approach to space exploration for decades without feeling the need to be seen as directly competing with the US in a manner akin to the US / Soviet space race.

With regards to astronomy, China is also looking to build its own version of the James Webb Space Telescope (JWST), with the first phase of the observatory being operational by 2024, and the completed facility operational by around 2030.

The project is to be led by the Peking University, but rather than being launched into space, this observatory will be Earth-based. Referred to as the  Expanding Aperture Segmented Telescope (EAST), the observatory will have a primary mirror similar to that of JWST, a 6-metre diameter made up of 18 individual hexagonal mirrors which work both individually and collectively to focus the light they gather into the secondary mirror for transfer back into the telescope and its instruments.

The site for the observatory is Saishiteng Mountain within the Qinghai Province on the Tibetan plateau, 4.2 kilometres above sea-level, well above the majority of the denser atmosphere, making it much easier for the telescope to also compensate for the distorting influence of that atmosphere.

But that’s not all; as an Earth-based telescope, EAST will be constructed in two phases. Once the 6-metre primary mirror system has been completed, and as funding allows, the addition of a further 18 mirror segments, increasing the mirror’s diameter to almost 8 metres; 1/3 as big again as JWST.

The cost estimate for the first phase of the observatory’s construction has been put at a mere US $69 million, with the expansion work – to be completed by 2030, as noted, to cost around a further US $20 million, compared to JWST’s estimated US $9 billion construction cost – although in fairness, EAST is an optical, rather than infra-red telescope, and so doesn’t require the need to operate at extremely lower temperatures, making it a lot less complex. When completed, EAST will be the largest optical telescope in the eastern hemisphere.

NASA Issues RFI Regarding Hubble Reboost

Since its launch in to a 540 km orbit above Earth in 1990, the Hubble Space Telescope (HST) has required regular “reboosting” as drag caused by friction contact with the tenuous upper atmosphere caused its orbit to decay. Up until 2009, these operations were completed by the US space shuttle as a part of scheduled HST servicing missions, with the very last mission serving to push HST to its highest orbit in anticipation of the shuttle being retired from active duty in 2011.

However, since then, atmospheric drag has reduced its orbit by some 60 km, and unless countered, it will force NASA to de-orbit HST in 2029/30 to ensure it burns-up safely and any surviving debris falls into the Pacific Ocean. By contrast, a re-boost mission could extend Hubble’s operational life by another 20 years.

To this end, in September 2022, SpaceX and billionaire Jared Isaacman – who has already funded one private mission to space using a Crew Dragon vehicle (Inspiration4) and is currently planning a further series of flights under the Polaris mission banner – started work on an unofficial mission outline to  rendezvous with HST and then boost its orbit. NASA then joined in these discussions on a non-exclusive basis or commitment to manage any reboost mission.

On December 22nd,  NASA issued a formal request for information (RFI) based on those discussions and exercising their non-exclusive nature to invite any interested parties to propose how a reboost mission might be completed, whether or not it expressly uses SpaceX hardware or some other, likely automated, booster vehicle. The RFI period is short, closing on January 24th, 2023, and the information gathered from respondents will be assessed over a further 6-month period and alongside the SpaceX / Polaris study to determine the best means of carrying out such a mission.

In this, there are both challenges and opportunities: HST is primarily designed to be serviced by shuttle, so by default it does have the capability to dock with the likes of SpaceX Dragon or other craft without the risk of damage. However, during the 2009 servicing mission, it was equipped with a Soft Capture Mechanism (SCM), a device primarily designed to allow a small automated vehicle attach itself to Hubble as part of a de-orbit mission. But with a suitable adapter, it might be used by a vehicle the size of Dragon to safely mate with HST and then ease it to a higher orbit.

Soyuz MS-22 Leak Update

The Russian space agency, Roscosmos, has stated it will conclude its investigation in to the status of Soyuz MS-22 towards the end of January 2023.

As I’ve reported in recent Space Sunday updates, the vehicle was used to carry cosmonauts Sergey Prokopyev and Dmitry Petelin and NASA astronaut Francisco Rubio up to the ISS in September 2022, where it has been docked ever since. However, on December 14th, 2022, the vehicle suffered an extensive ammonia coolant leak, potentially crippling it.

The exact cause of the leak has yet to be determined, although Roscosmos remains convinced it was the result of either meteor dust or a tiny piece of space debris impacting the Soyuz coolant radiator, puncturing it. However, their focus has not been on determining the cause of the leak, but in trying to determine whether or not the vehicle is capable of returning the three crew to Earth safely, or if a replacement vehicle will be required.

As I noted in my previous Space Sunday update, should Roscosmos decide a replacement vehicle is required to return Prokopyev, Petelin  and Rubio to Earth, it will likely be Soyuz MS-23, which would be launched in February 2023 to make an automated rendezvous with the space station. However, it is now being reported that NASA has also contacted SpaceX to assess the feasibility of using Crew Dragon to return some or all of the MS-22 crew to Earth.

In this, it is unclear as to precisely what NASA has requested of SpaceX, and neither party is commenting. One theory is that the request is to determine whether the current Crew Dragon vehicle currently docked at ISS could carry additional personnel to Earth, if required. Another is NASA wishes to access the potential of launching an uncrewed Dragon to the station as a means to act as an emergency back-up for evacuation of the station – should it be required – prior to MS-23 being available to launch.

Both options are long-shots; getting Crew Dragon vehicle and its Falcon 9 rocket ready for launch in advance of MS-23 – a mission already in preparation, regardless of whether it flies with its planned crewed or uncrewed – is not an easy task. Further Dragon isn’t equipped to handle Russian space suits, the kind used by Prokopyev, Petelin  and Rubio. As such, to even consider Crew Dragon as temporary lifeboat  – much less a replacement for MS-23 to bring the three crew back to Earth – would require not small modification to its support systems. Similarly, while the Crew 5 vehicle might be able to return one or two of the MS-22 crew to Earth should it be necessary to do so, there is also the no insignificant matter of getting its life support systems to work with the Russian space suits.

One particular area of concern is that a number of experts outside of NASA / Roscosmos have opined that whatever Roscosmos may announce at the end of January, MS-22 is unlikely to be safe to bring its crew home. Therefore, should Roscosmos opt to do so, NASA might opt to look to other means to return astronaut Rubio to Earth as a matter of safety.