SPACEFLIGHT Exploration of Mars
Invaders to Mars!
Dr ADAM BAKER FRAeS, Professor GUGLIELMO AGLIETTI FRAeS, RICHARD LOWE MRAeS and PAT NORRIS FRAeS from the RAeS Space Group describe the three probes now heading for Mars – and one that’s not.
NASA’s Curiosity Mars Rover has now been on the Red Planet for eight years.
There may not be a ‘race to Mars’ but there is plenty of national prestige hanging on the success of the three space probes currently en route to the Red Planet. The US and China will both put rovers on the surface, the American one outfitted with a small helicopter – a first on Mars – while the United Arab Emirates (UAE) will place their probe in orbit above the planet, as will the Chinese. We first look at why Mars is such a popular destination and what it takes to get there, then look at each of the three probes, ending with one (European) that has not made it (yet).
Why Mars?
Mars has the most Earth-like surface conditions of any nearby planet. However, ‘most Earth-like’ is still quite hostile. The atmosphere is thin and nonbreathable carbon dioxide; temperatures drop to –100°C at night; and oxidising dust is widespread. Closed life support systems are needed to walk on Mars’ surface. Even so, life may have existed previously and inhabited Mars’ surface – which was once warmer, with a thicker atmosphere and liquid water. Today, some robust forms of simple life may still exist, well hidden where local conditions favour it.
Life on Mars is unlikely to reveal itself on our current missions, which continue to map Mars from orbit in a range of wavebands while only exploring a tiny fraction of the surface from the ground. If life evolved and then died out on the Red Planet, then fossil records may remain where prehistoric oceans once were.
Finding a fossil record will have profound implications for our theories of how life evolved in our solar system, pointing to a greater likelihood of life elsewhere in the Universe. This might also trigger humanity to seriously consider Mars as a future second outpost of humanity. Early human visits may be brief but Mars’ subsurface water, ice and solar energy resources can support longer term human habitation. This may involve geoengineering or ’terraforming’, requiring improved interplanetary transportation infrastructure, and command of greater energy resources than today. Sorry Elon, it’s going to be some time yet before we can live on Mars permanently… but keep building those rockets!
How to explore Mars
Why are rockets fundamental to our exploration of Mars? Rockets enable travel between the separate orbits of Earth and Mars, whose alignments restrict efficient or ‘minimum energy’ transfers to narrow ‘windows’ every two years. Transfers to Mars require about 1/3 more energy compared to reaching Earth orbit from the ground. When a spacecraft reaches Mars, it can briefly fly past taking images or video, as did the earliest probes; or rendezvous and go into orbit around the planet. Rockets for decelerating are also needed for rendezvous as Mars travels more slowly than Earth around the Sun. On reaching Mars, spacecraft have the option of landing on the surface, requiring further rocket propulsion. Since October 1960, almost 50 missions, some comprising orbiters and landers have targeted Mars. Unfortunately, only around 50% of landers have succeeded: the USSR’s Mars 3 landed and operated for only two minutes before going silent in 1971: the UK’s Beagle 2 was lost during landing in 2005 but subsequently identified intact on the surface in 2015. This low success rate arises in part from Mars’ thin atmosphere, which is not substantial enough to sufficiently slow descent with parachutes alone as on Earth but is thick enough to significantly increase the complexity and risks of landing.
NASA’s Perseverance rover
NASA’s latest mission builds on the earlier success of the Curiosity rover mission (launched in 2011). Perseverance is based on the same design concept, taking advantage of both lessons learned and parts available from the earlier mission. The result is a vehicle with the size and weight of a small car, weighing in at just over 1tonne and powered by plutonium. It will also reprise Curiosity’s dramatic ‘Sky Crane’ descent system. Following the main highspeed descent phase, a ‘Jet Pack’ will gently lower the rover onto the surface.
UAE’s Hope probe. UAE Space Agency
The rover’s plutonium-based radioisotope thermoelectric generator (RTG) provides all the power needed for the mission, allowing Perseverance to operate continuously through Mars’ day-night cycle and seasons.
Complementing a wide range of cameras, Perseverance carries microphones that will capture sound during descent and while exploring the surface, treating us to the sounds of Mars.
The mission launched successfully on 30 July 2020 and is scheduled to land on Mars in late February 2021.
China’s Tianwen-1
China’s Chang’e 4 lander and its Yutu-2 rover have been exploring the surface of the farside of the Moon since 3 January 2019, the first probes to do so. Having demonstrated world-leading exploration credentials on the Moon, the China National Space Administration has expanded its horizons to Mars, and Tianwen-1 now on its way there will give it ‘Red Planet pioneer’ status as the first ever combined orbiter, lander and rover mission.
China’s Tianwen-1 lander. UAE Space Agency
Tianwen-1 will enter a 265km by 1,200km polar orbit in February 2021. The 3.2 tonne Orbiter, with a design life of two years, contains seven scientific instruments to analyse the surface of Mars and its space environment – high resolution (~1m) and medium resolution (~100m) cameras, a magnetometer (in collaboration with the Austrian Research Promotion Agency (FFG)), an ion and neutral particle analyser, a high-energy particle analyser, a spectrometer to study the mineralogy of Mars and a subsurface radar.
The Lander and its Rover will stay attached to the Orbiter in space for two or three months after arrival at Mars to allow time to refine the choice of landing site – a tactic employed by NASA’s Viking landers in the 1970s. Two possible sites (each defined by a 100km by 40km ellipse) have been chosen in Utopia Planitia, a ~3,000km x 3,000km region centred on about longitude 115°, latitude 45°N, within which Viking-2 touched down in 1976.
The 1-3 tonne Lander (carrying the 240kg Rover) will use a combination of a heat shielding capsule, a parachute and a 7,500 newton retro-rocket to burn off entry speed and make a soft landing, then deploy a ramp for the Rover to descend. The Rover incorporates six scientific instruments to analyse mineralogy and atmosphere: a multispectral camera, a navigation/topography camera, a ground-penetrating radar able to image 100m below the surface, a laser-induced breakdown spectroscopy instrument (similar to the LIBS instrument on NASA’s Curiosity’s), a magnetic field detector and a meteorology package. The ground-penetrating radar will not only analyse near-surface geological structures but also search for underground pockets of water. For the spectroscope instrument, France provided a calibration target that duplicates the one on Curiosity, with the intention of allowing a rigorous comparison of the two datasets.
About twice the size of the Chang’e Moon rovers, the Tianwen-1 Rover is a six-wheeled, solar powered, 2.0 × 1.65 × 1.85m vehicle with a design life of 90 Martian days (92.5 Earth days). It will communicate direct with Earth and via the Orbiter.
The launcher
On 23 July 2020 at 12:41 local time (04:41 UTC) the holiday crowds enjoying a sunny afternoon on the beaches of China’s sub-tropical Hainan Island cheered as the Long March 5 (LM5) rocket carried the 4-9 tonne Tianwen-1 assemblage aloft. The launch time had not been announced in advance but live streams of the event were broadcast over social media by several of those in the area. LM5 is the heavy-lift member of China’s new generation of launch vehicles capable of placing a 25 tonne payload into low Earth orbit. Its core rocket motors are fuelled by liquid hydrogen and liquid oxygen illustrating that this generation is the first not to be derived from missile technology (previous LM rockets used hypergolic fuels that could be stored for long periods at room temperature). This was the fourth launch of LM5 and there has also been one of the closely related LM5B.
The launch trajectory took the rocket south east over the Philippines close to Manila (some might say too close from a safety perspective). During the six month cruise to Mars, Tianwen-1 will make two or three course corrections using its onboard propulsion system. The European Space Agency (ESA) provided tracking for the spectroscope support for the early phases of the flight and the Argentinian Space Agency (Conae) is supporting it by way of a Chinese-run tracking station installed in that country. The logos of the four international collaborators (ESA, Conae, CNES (France) and FFG) were emblazoned on the LM5’s fairing.
As with the Chang’e (Moon Goddess) probes, China has made reference to its ancient literature with the name Tianwen – it means ‘questions to the heavens’ after the poem of that name by QuYuan (3rd Century BC) that asks philosophical questions including how the Universe was created. If the Moon probe naming policy is followed, we may expect the separate Orbiter, Lander and Rover to be given specific names with a similar cultural theme as the mission progresses.
Looking to the future, not content with sending probes on a one-way trip, China plans to bring samples back to Earth from the surface of the Moon in 2021, then from an asteroid in the mid-2020s and finally from the surface of Mars at the end of the decade.
UAE’S Al-Amal
In the last few years, the UAE presence in the space sector has grown significantly, with eye-catching participation in international conferences and other high-profile initiatives.
After having successfully put three Earth observation satellites into orbit, the current Mars Mission Al-Amal, also known as Hope, is timed to arrive at Mars just before the 50th anniversary of the country’s independence, giving the UAE a leadership position in the Arab world for this sector. Besides the international prestige, the mission aims to catalyse interest and develop new capabilities for UAE industry and academic institutions, to ultimately grow their wider high-tech sector.
The development of the $200m mission (excluding the cost of the operations), has been led by the UAE’s Mohammed bin Rashid Space Centre (MBRSC), and the spacecraft was built in partnership with the Laboratory for Atmospheric and Space Physics (LASP), at the University of Colorado, Boulder. The three instruments that are carried by the craft also had UAE scientists and engineers working in partnership with staff from Arizona State University and the University of California, Berkeley, fostering knowledge transfer and growing local UAE capabilities.
The spacecraft, which weighs 3,000lb (1,361kg) and measures 2.9m in length by 2.4m width, was successfully launched from the Tanegashima Space Center, in Japan, on a Mitsubishi Heavy Industries’ H-IIA rocket at 21:58 UTC Sunday, 9 July 2020. Later, mission control communicated that the spacecraft had successfully separated from the rocket, reconfirming the reliability of this vehicle. The operation of this rocket was privatised in 2007, transferring production and launch services from JAXA to Mitsubishi and, since 2003, 36 launches were successfully performed.
Currently, on its way to Mars, the spacecraft is due to acquire a semi-synchronous orbit around the planet at an altitude between 20,000km and 43,000km, with a velocity similar to that of the surface of the planet. This will enable prolonged observations of areas of the planet with the objective to study the dynamics of its atmosphere.
ExoMars
The European Space Agency (ESA) and Russian Space Agency (Roscosmos) also plan to place a rover on Mars through the ExoMars programme. ESA’s Rosalind Franklin rover, built in Stevenage in the UK, will be carried to the surface by Roscosmos’ Kazachok (‘Little Cossack’) descent system.
A successful Mars rover mission would be a big result for ESA, Roscosmos and the UK in particular. ESA has achieved major exploration successes through probes such as the Huygens lander (Saturn’s moon, Titan) and Rosetta (comet exploration) but ExoMars carries its first rover. The UK has some pride to recover following the ill-fated Beagle-2 lander (also UK-built, which accompanied the otherwise highly successful ESA Mars Express orbiter). Roscosmos can also take this mission as a big opportunity for Russia to re-assert its earlier capabilities. The path to Mars has been a graveyard for many missions. The USSR successfully placed just one lander on the surface (‘Mars 3’, 1971) – which failed just 14-5secs into its first image transmission.
Kazachok and Rosalind Franklin were originally scheduled for launch during the summer of 2020. Unfortunately, difficulties with the parachute descent system could not be resolved in time to maintain the schedule. The launch is now expected to take place in 2022 (the next time that Earth and Mars’ orbits will bring them into the right positions).
Arrival Feb 2021 – then what?
All three probes (US, UAE and China) will coast for about six months to Mars, arriving in February 2021. Tianwen-1 and Al Amal will manoeuvre themselves into orbit around the planet, while Perseverance will descend straight to the surface. The nerve-wracking tension of a Mars descent will be heightened by video beamed by its downward-pointing camera back to Earth. It will be April or May 2021 before Tianwen-1 descends from orbit to the surface and it remains to be seen if China will announce the landing date in advance.
With so much attention – and technical capability – being focused on Mars, the 2020s may be a tipping point in its exploration. A sustained and successful programme of orbiters, landers, rovers – and helicopters – on Mars will make the solar system start to feel just a little bit smaller.