Europe finally in orbit around Mars

Theme Park Mars

Imagine being a young child going to your favorite theme park. After being promised for months by your parents you and your little brother are go. You drive 1000 km just to get there and see that big roller coaster in the distance. Your heart starts pounding with anticipation, only to hear that for the next two years you first have to drive circles around the parking lot before you are allowed to get closer. You’d be underwhelmed and your parents better have a good reason… Worse: two years ago they sent in your little brother first and he was never heard of again. The little Sherlock you are, and bored as hell, this requires some serious sniffing around.

That is exactly what happened to the ExoMars probe (Exobiology on Mars) that ESA and RFSA, the Russian Space Agency, sent to MARS.

And it was on purpose:

Patience has its own rewards

Launched March 14, 2016 on a Russian Proton rocket, The ExoMars Trace Gas Orbiter  (TGO) arrived at Mars in October 2016, to investigate the potentially biological or geological origin of trace gases in the atmosphere. It will also serve as a relay, connecting future rovers on the surface with their controllers on Earth. On its back, it carried its little brother Schiaparelli, a small probe testing European landing technology.

A suite of four science instruments will make complementary measurements of the atmosphere, surface and subsurface. Its camera will help to characterize features on the surface that may be related to trace-gases sources, such as volcanoes.

It will also look for water-ice hidden just below the surface, which along with potential trace gas sources could guide the choice for future mission landing sites.

These are the four instruments:

1. NOMAD: The Nadir and Occultation for Mars Discovery, developed by Belgium, has two infrared and one ultraviolet spectrometer channels.
2. ACS: The Atmospheric Chemistry Suite , developed by Russia, has three infrared spectrometer channels. NOMAD and ACS will provide the most extensive spectral coverage of Martian atmospheric processes so far. Detection of atmospheric trace species, clues for Methane produced by a biological origin, at the parts-per-billion (ppb) level will be possible.
3. CaSSIS: The Colour and Stereo Surface Imaging System , developed by Switzerland, is a high-resolution, 4.5 m per pixel (15 ft/pixel), color stereo camera. It will build accurate digital elevation models of the Martian surface, which is also an important tool for characterizing candidate landing sites for future manned missions.
4. FREND: The Fine-Resolution Epithermal Neutron Detector, developed by Russia,is a neutron detector that can provide information on the presence of hydrogen, in the form of water or hydrated minerals, in the top 1 m (3 ft 3 in) of the Martian surface.

Sniffing for life

Particularly, the mission will characterize spatial, temporal variation, and localization of sources for a broad list of atmospheric trace gases.

If methane (CH4) is found in the presence of propane (C3H8) or ethane (C2H6), that will be a strong indication that biological processes are involved. However, if methane is found in the presence of gases such as sulfur dioxide (SO2), that would be an indication that the methane is a byproduct of geological processes. (*)

But before any of this could get underway, the spacecraft had to transform its initial, highly elliptical four-day orbit of about 98 000 × 200 km into the final, much lower and circular path at about 400 km. From the parking lot, to the entrance gate, so to speak.

And it took a long time.

Slowing a car with a breath of air

The method used is called aerobraking. To conserve as much propellant as possible, the TGO slows down rubbing against Mars’s upper atmosphere on each pass it makes on its elliptical path. And this is a delicate maneuver: too steep an angle and you burn up. That is the reason why only a small amount can be bled away on each pass and why it took two years to complete the maneuver.

In numbers: According to ESA, the thin upper atmosphere provides only gentle deceleration – at most some 17 mm/s each second. How small is this?

If you braked your car at this rate from an initial speed of 50 km/h to stop at a junction, you’d have to start 6 km in advance.

“Over a year, we’ve reduced the speed of the spacecraft by an enormous 3600 km/h, lowering its orbit by the necessary amount,” says TGO spacecraft operations manager Peter Schmitz.

The approach used means the probe has plenty of remaining propellant for future use and potential mission extensions.

As a result, it was only on on 20 February at 17:20 GMT, when the craft fired its thrusters for about 16 minutes to raise the closest approach to the surface to about 200 km, well out of the atmosphere. This effectively ended the aerobraking campaign, leaving it in an orbit of about 1050 × 200 km.

The 21st of February 2018, ESA finally sent out its press release with the triumphant title, “SURFING COMPLETE”.

“During some orbits, we were just 103 km above Mars, which is incredibly close.“

Are we there yet?

In the next month, the control team will command the craft through a series of up to 10 orbit-trimming maneuvres, one every few days, firing its thrusters to adjust the orbit to its final two-hour, circular shape at about 400 km altitude, expected to be achieved around mid-April.

The initial phases of science gathering, in mid-March, will be devoted to checking out the instruments and conducting preliminary observations for calibration and validation. The start of routine science observations should happen around 21 April.

“Then, the craft will be reoriented to keep its camera pointing downwards and its spectrometers towards the Sun, so as to observe the Mars atmosphere, and we can finally begin the long-awaited science phase of the mission,” says Håkan Svedhem, ESA’s project scientist, on the ESA website

Of course, that much patience is inhumane. Over the course of the past two years, the instruments had been tested on occasion and already showed us surprising

And what happened to its little brother?

Schiaparelli, the landing experiment the size of a living room table failed on 19 October 2016. Something that happens a lot when you try to land on Mars for the first couple of times.  A British probe, Beagle 2, already landed in 2003 but failed to open its solar panels and communications antenna properly. It took two years of suspense before an American Mars orbiting probe in 2005 took pictures demonstrating this was the case.

Schiaparelli failed more spectacularly: Using its thrusters it first came to a perfect standstill and then still managed to crash. This is because its sensors got confused which resulted the probe coming to a vertical standstill far above the surface.

A nightmare for the nail-biting engineers having labored with passion on the design, it all comes down to sensor fog.  Only to see it end with a bitter taste in a somewhat slap stick fashion. Wile E. Coyote , the comical Looney Tunes cartoon character  from the Warner Bros Studios, who often finds himself hanging midair above a canyon, while unsuccessfully hunting the road runner, couldn’t have executed the maneuver any better.

But this analysis wouldn’t do the little lander justice. The thrusters and heat shield worked perfectly. These items can now be erased from the European R&D to-do list.

Europe is not throwing in the glove, far from it. It is even raising its ambitions.

Peeking under ground

A long time in the making and less than three years from now, one of ESA’s most ambitious scientific endeavors will blast off in 2020, and head for the planet Mars. If all goes according to plan, the European-built 2020 ExoMars rover and a Russian surface platform will be delivered safely onto the planet’s orange, dusty plains in 2021.

The orbiting TGO will serve as its data communications relay while the ExoMArs rover searches for signs of past life.

It will be the first probe ever to drill down into the martian soil, 2 meters deep to look for microbes and characterize the layers of soil. A first for Europe.

ExoMars rover, you read the instructions: land safely.

Thumbs up.

Sources:

• ESA website: press article, 21 February 2018, SURFING COMPLETE
• ESA website: press article, 05 September 2017, A WINDOW ON THE EXOMARS ROVER’S SEARCH FOR MARTIAN LIFE

Footnote:

(*)Methane:

The nature of the methane source requires measurements of a suite of trace gases in order to characterise potential biochemical and geochemical processes at work. The orbiter has very high sensitivity to (at least) the following molecules and their isotopomers: water (H2O), hydroperoxyl (HO2), nitrogen dioxide (NO2), nitrous oxide (N2O), methane (CH4), acetylene (C2H2), ethylene (C2H4), ethane (C2H6), formaldehyde (H2CO), hydrogen cyanide (HCN), hydrogen sulfide (H2S), carbonyl sulfide (OCS), sulfur dioxide (SO2), hydrogen chloride (HCl), carbon monoxide (CO) and ozone (O3). Detection sensitivities are at levels of 100 parts per trillion, improved to 10 parts per trillion or better by averaging spectra which could be taken at several spectra per second.

• Thomas, I. R.; Vandaele, A. C.; Neefs, E.; et al. (2017). “The NOMAD Spectrometer Suite on the ExoMars 2016 Orbiter: Current Status” (PDF). The Sixth International Workshop on the Mars Atmosphere: Modelling and Observation. 17-20 January 2017. Granada, Spain. Bibcode:2017mamo.conf.4401T.
• Montmessin, F. “Atmospheric Chemistry Suite: Science Overview” (PDF). LATMOS CNRS, France. p. 44. Retrieved 14 March 2016. Determining the origin of methane on Mars can only be addressed by looking at methane isotopologues and at higher alkanes (ethane, propane).
• McKie, Robin (20 February 2016). “‘Giant nose in the sky’ ready for lift-off in mission to sniff out traces of life on Mars”. The Guardian. Retrieved 21 February 2016.
• Vandaele, A. C.; et al. “NOMAD, a spectrometer suite for nadir and solar occultation observations on the ExoMars Trace Gas Orbiter” (PDF). Institut des NanoSciences de Paris. Retrieved 4 September 2015.