After nearly all hope was lost, the silence of the Fobos-Grunt spacecraft has been broken, following a major breakthrough via a European Space Agency (ESA) tracking station in Perth, Australia. With the earlier confirmation a carrier signal having been established during one pass, the pace of progress is picking up, with news that received telemetry data is now being analysed.
Fobos-Grunt – The Problem:
Fobos-Grunt – which was also hosting China’s first Mars probe, Yinghuo-1 as a passenger – enjoyed a nominal launch via a Zenit-2 launch vehicle, which occurred at 02:16 local time on November 8 from the Baikonur Cosmodrome.
Fobos-Grunt was launched with a primary mission of conducting a sample-return effort from Mars’ larger natural satellite, Phobos. The spacecraft was designed as the third dedicated mission to Phobos, the previous two missions, Fobos-1 and Fobos-2, were launched in 1988 by the Soviet Union. However, both failed.
In total, all of the previous 16 Russian missions to the Red Planet since the 1960s have failed – the latter of which was the Mars-96 spacecraft, which saw its mission ended prematurely in a launch failure.
With a mass of 13,500 kilograms, Fobos-Grunt is the largest planetary spacecraft ever built in the former Soviet Union and was to be the first sample return mission to the natural satellite of another planet, and the first such mission to be conducted by Russia.
The two-stage Zenit lofted Fobos-Grunt into orbit via the first stage’s single RD-171M engine and second stage’s RD-8 vernier engine and RD-120 main engine – both of which performed nominally. Following shutdown of the second stage main engine, Fobos-Grunt separated, and solid rocket motors on the second stage fired to increase the separation distance between the spent stage and the payload.
Fobos-Grunt was set to perform an orbit-raising manoeuvre two and a half hours after launch, prior to a second burn 126 minutes later, which would have taken it into heliocentric orbit to begin its journey to Mars. Both burns failed to materialize.
The reason for the lack of a burn from the cruise stage – derived from the Fregat stage, powered by an S5.98M engine using unsymmetrical dimethylhydrazine as propellant and nitrogen tetroxide as an oxidiser – is still not fully understood.
The lack of fault information is mainly due to the failed efforts by Russian controllers to re-establish a link with the spacecraft, in order to receive vital telemetry, or indeed send commands to aid such a process.
Among the challenges associated with communicating with Fobos-Grunt during passes over ground stations was believed to be a potential blockage by the yet-to-be-used fuel tank of the low gain antennas. This tank – located on the aft of the cruise stage – would be expended and released in the event of both burns being completed. It is understood the spacecraft was never designed to be commanded prior to these two burns.
Fobos-Grunt – The Breakthrough:
However, on Tuesday evening, a breakthrough was achieved with the help of European Space Agency (ESA) assets.
Reported by the European Space Operations Centre (ESOC) in Darmstadt, Germany early on Wednesday, contact – the first observed since Fobos-Grunt’s launch – was received by ESA’s tracking station at Perth, Australia at 2025 GMT on Tuesday.
“Upon request from NPO Lavochkin, operator of the mission on behalf of the Russian space agency, Roscosmos, ESA agreed to do its utmost to attempt contact using the Agency’s ground station network,” noted an ESA statement on the breakthrough, with the attempts including modifications to the 15m dish.
It was the modification to the dish, a last gasp effort to establish a link with Fobos-Grunt, which broke the silence, after previous attempts – including those of ESA – to communicate with the spacecraft. However, this initial success did not include the downlink of telemetry.
“Starting on November 9, and in close coordination with Russian engineers, ESA made almost daily attempts to contact Phobos-Grunt using numerous configurations and radio link modes, but to no avail. A major problem was that the spacecraft’s orbit was not accurately known, whereas ground stations normally require very accurate position information for pointing due to the antenna size,” added ESA.
“In the past few days, ESA’s 15 m-diameter Perth dish was modified by the addition of a ‘feedhorn’ antenna at the side of the main dish so as to transmit very low-power signals over a wide angle in the hopes of triggering a response from the satellite.
“The transmit power was reduced in part because the receiver on Phobos-Grunt is optimised to receive only very weak signals when deep in space. Perth is ideally located because the satellite’s solar panels were illuminated by sunlight when overhead, giving a power boost to its systems.
With very short windows of opportunity to send communications to Fobos-Grunt as it raced overhead in Low Earth Orbit (LEO), controllers only had a matter of minutes to send commands, which related to switching on the the spacecraft’s transmitter and send a confirmation signal back..
“Owing to its very low altitude, it was expected that our station would only have Phobos-Grunt in view for six to ten minutes during each orbit, and the fast overhead pass introduced large variations in the signal frequency,” said Wolfgang Hell, the Phobos-Grunt Service Manager at ESOC.
During the Tuesday evening attempt, this was seen to be a success – leading to the received data being transmitted from Perth to Russian mission controllers, via ESOC for analysis.
Vitally, this successful process raised hopes of being able to replicate the link, which also proved to be successful on a later pass, as confirmation of a successful downlink of abbreviated telemetry was noted.
With numerous passes, opportunities to learn more about the spacecraft’s health have since increased, such as reports the flight computer may be switching in and out of safe mode, when out of the line of sight with the sun.
Following the Perth dish’s success, it may also be possible to replicate the method employed at another ground station – potentially at ESA’s Maspalomas Station, located at the Canary Islands, which hosts a 15-metre antenna with reception in S- and X-Band and transmission in S-band.
As far as the potential recovery efforts, it is unlikely the spacecraft can be sent on its primary mission to Phobos, given its window of opportunity has now elapsed – at least from a complete mission standpoint. It may be possible to carry out an alternative mission profile, but no official notes of such evaluations have been released.
Continued commanding link successes would also likely lead to a level of control for any extended stay in Low Earth Orbit (LEO), or for a controlled re-entry.
UPDATE: Further communications were made between Wednesday and Thursday, although the telemetry is understood to be incomplete and “garbled” – requiring a large amount of work to gain data from.
There are many conflicting reports, mainly based around the quality of the telemtry and how much data has been gathered. Russian media have reported that a second dish – at the Baikonur Cosmodrome – has been in contact with the spacecraft on Thursday.
With several passes per day, this is a developing story. Refer to the live update pages. Additional notes of interest will be added to this article.
(Images: Via Roscosmos and ESA)