The journey is epic—over 600 million kilometres—but it’s the next two days that will be decisive for Mangalyaan, as it approaches Mars.
BY G B S N P VARMA
IMAGES COURTESY ISRO
India: 07:17:32, September 24, 2014.
The time of the day when hardships are not yet known, hopes not yet exhausted, dreams not yet broken.
You walk your dog, or the other way round. You get ready for breakfast. You’re ready to go out. Go to school. You go to your cattle into the fields. Or, maybe, you just crashed out of dreams.
Miles from where you are, the engineers and scientists of Indian Space Research Organization (ISRO) are peering into their consoles, some staring at the giant screen at the back of their consoles in ISRO Telemetry, Tracking and Command Network (ISTRAC) in Peenya Industrial Estate, Bangalore. Some distance away, the people at ISRO’s Indian Deep Space Network (ISDN) at Byalalu, Bangalore, cannot yet listen in on the Mars Orbiter Mission (MOM), but they are excited too.
Some have not slept at all the last night. Some took a cosmic perspective and slept soundly. They rose early, maybe at about 2 a.m., bathed, and prayed, for they knew not what the day would hold. They practised their rituals—as they had done since the beginning of the mission—marking their foreheads with vermilion and sacred ash. They shaved; some didn’t for “lucky beard”. Atheists, presumably a minority among them, bellowed their wishes into the vast space, believing—at last and at the moment—that the cosmos has the power to make things happen.
It’s 07:17:32, the big T, September 24, 2014. The Liquid Apogee Motor (LAM) onboard Mars Orbiter Mission (MOM) starts firing. Minutes tick by, each one an eternity.
Thirty-and-a-half minutes later, if all goes well, the DSS-34 (a 34-metre antenna) in Canberra Deep Space Network, Australia, will listen in to what MOM is saying. Relayed from there to ISTRAC, the ground computer will measure the total performance of the burn, calculating how much change in velocity took place, how much the spacecraft has decelerated.
The spacecraft is then inserted into Mars’ orbit.
For people back on earth, the spacecraft just transported more than its equipment, instruments and itself. ISRO’s epic voyage of designing, building, and sending a spacecraft on an interplanetary mission, of India joining the fraternity of countries and groups of countries—the United States of America, Europe and Soviet Union—is now real.
The interplanetary mission consists of three phases: geo-centric phase, heliocentric phase, and Mars-centric phase. Essentially, three frames of reference, and each comes with its own dynamics.
“When we launch, we don’t launch the spacecraft directly to Mars. We launch it at a low orbit. We cannot give it the speed to go to Mars; it should be given incrementally. We launch it at some altitude and keep increasing the speed. Eventually the speed is so high that it leaves the earth’s orbit,” explains Dr Hari B. Hablani, a professor of aerospace engineering at IIT Bombay. He earlier worked for Boeing and his areas of expertise include “satellite-based navigation, spacecraft guidance and navigation for rendezvous, guidance and control of interplanetary spacecraft”, among others. Hablani is not associated with MOM.
During the process of these manoeuvres, propellant is burnt, becoming a dead mass. The containers carrying it are jettisoned so that the spacecraft can be lighter.
As the spacecraft travels out of earth’s orbit, the gravitational force of the earth weakens. “You go twice the distance from the centre of the mass of the earth, the gravitation force weakens by one-fourth,” Hablani explains.
If you were riding the spacecraft, moving out of the earth’s orbit and being freed of its gravitational pull, it would feel like a free fall. You’re not going to smack into anything because the trajectory of your fall is such that it approximately equals the curvature of the earth. The manoeuvres raise the altitude of the trajectory, which is necessary until you and your spacecraft are out of earth’s gravity.
Now the spacecraft has left the earth’s sphere of influence and is in the heliocentric phase—going toward Mars with the help of the sun’s gravity.
In every mission, all of this must happen with the right velocity in the right direction. It doesn’t happen automatically, though, because the geometry keeps changing. The earth, spacecraft, Mars—all are moving. The mission engineers chart the direction and give it the requisite velocity so that when the spacecraft reaches Mars, Mars is right there.
“It’s like meeting a friend who is also travelling. You make sure you go meet your friend when he reaches there, not before or after,” Hablani explains.
In the next phase, when the spacecraft is in the neighbourhood of Mars— and MOM is currently on the verge of it—Mars’ gravity becomes more important than the sun’s. To be captured by Mars, the spacecraft has to have the right velocity so that Mars’ gravity will be able pull the spacecraft toward itself. If there is too much velocity, the spacecraft will go past Mars.
Therefore, reducing the spacecraft’s speed and orienting it—that’s what mission engineers will do on September 24.
Different forces pummel the spacecraft in its different phases. Near the earth, it’s mostly gravity. Solar radiation is minute. Atmospheric drag occurs while in earth’s atmosphere. Then in the heliocentric phase, it’s pulled by the sun’s gravity, and is subjected to the sun’s rays. Space environment exerts pressure. Since the sun’s rays continually fall on the spacecraft, one side gets hot, the other side cold, leading to thermal stresses. That’s when heat transfer becomes important. Equipment and instruments should be protected. So, solar radiation-hardened material is used to insulate equipment on board from thermal stresses.
The changing geometry has a bearing on communication and power systems onboard. The solar array should always be perpendicular to the sun’s rays, and the antenna should be pointed to the Deep Space Network (DSN) so that people on the ground can know its whereabouts. Since all are moving—the earth rotates 90 degrees around the sun in three months—the sun starts looking at a different part of the spacecraft rather than toward the solar array. Similarly, the antenna may look away from DSN.
“These are all general problems every spacecraft will have,” says Hablani. This is where attitude control comes in, which is controlling the orientation of the spacecraft. This is monitored continuously by engineers back on earth, who orient it as necessary.
“Engineers already designed the path,” he says. They have a reference trajectory of the spacecraft. They keep calculating where the spacecraft is, the speed with which it’s going and the direction in which it’s going, to know the actual trajectory. The two trajectories are constantly compared. If the difference is too large, mid-course corrections are done. On September 24, MOM should be in the orbit they desire.
When MOM is in the desired orbit, it won’t feel lonely up there. Already, orbiters—NASA’s Mars Reconnaissance Orbiter and Mars Odyssey, and European Space Agency’s (ESA’s) Mars Express—and rovers—NASA’s Opportunity and Curiosity—are at Mars.
What’s more, NASA’s Mars Atmosphere and Volatile Evolution Mission (MAVEN) is now orbiting Mars. After hurtling through deep space nearly a year, MAVEN fired its six MOI rocket motors for a 30-minute burn. It then decelerated enough to be pulled in by Mars’ gravity.
In an earlier email to Fountain Ink, MAVEN’s principal investigator Bruce M. Jakosky, of the University of Colorado, Boulder, said: “We’ve had many successful spacecraft missions to Mars, going back to the 1960s. This means that we know a lot about Mars and we are able to ask increasingly detailed questions about the Mars environment. To me, a key point about Mars is that one cannot investigate a part of the system in isolation from other parts. The atmosphere interacts with the surface and with the subsurface, and also with the upper atmosphere and, there, with the sun and the solar wind. Key questions about the Martian climate or about the potential for life require knowledge of the history of volatiles, and that is the focus of the MAVEN mission. We’re focused on understanding the role that loss of gas out the top of the atmosphere has played in the history of the atmosphere. This result will have implications for understanding the history of the climate, of the geology of the surface, and of the potential for life.”
Many of the Mars missions are star-crossed. Jakosky said, “Mars missions are inherently difficult—even the US does not have a great success rate. In the ‘modern’ era of Mars missions subsequent to the Viking missions of the 1970s, we’ve had 7 successful spacecraft and 5 failures. For any one mission, there are 10,000 things that have to go right, and if only one of them goes wrong we could lose the mission. We’re working hard to ensure that each of these 10,000 things has been done right, has been tested, and will lead to success for us on Sunday (US time).”
Speaking of possible collaboration between the two missions, he says, “The MOM mission carries instruments that make measurements that are relevant to understanding the Mars upper atmosphere. As a result, there will be real value in analysing the results together or in combining results from both missions to get a better understanding of the overall Mars system and of the processes that are going on today. We have not yet developed detailed plans for how we would utilise both data sets together. I anticipate that this will happen once both spacecraft are safely in orbit at Mars.”
Now that MAVEN is in Mars orbit, their efforts are vindicated.
When the project first kicked off, people involved in the mission had no idea how all-consuming it would turn out to be. They lived it for 15 months, designing and building, before it was sent off into space. It didn’t end there: they fuss over its health, trajectory and behaviour, now that it’s in space. To them, the Mars orbiter is not a physical construction barrelling through space, but also a metaphysical payload.
Dr S. Arunan is the project director of MOM, and is keeping abreast with both aspects of the payload.
“We’re very hopeful,” he says, “everything has gone well so far, and we expect the orbit insertion manoeuvre to go well on 24th.”
His office room is remarkably free of clutter. A collection of gods and goddesses rests on a table nearby his chair: Saraswathi, Shirdi Sai Baba, Vinayaka, and others. Yellow and orange flowers are placed at each. A facsimile of MOM stands on a stool next to the shrine—scale 1.5, wrapped in bright yellow wrapper, with antenna on one side and solar array on the other. Another facsimile, scale 1.20, sits on his broad desk. The walls are festooned with posters of MOM’s travel path, the instruments on it, and others.
The mission has become a part of him. While building MOM, Arunan almost lived here, going home occasionally. He paces the aisles and corridor on the fourth floor of ISAC, talking on the phone, before returning to his office and sitting down.
For sending the spacecraft out of the earth’s orbit, he says, they had narrower specifications. In contrast, to manoeuvre it into the Mars orbit, they have wider specifications, and so it’s much easier.
The orbital manoeuvre starts much earlier, in the wee hours of September 24. Three hours—04:17:32 (T-3 hours)—before the LAM starts firing, a medium-gain antenna takes charge of communication with earth. It’s time when the solar arrays, telecommunication systems, sensors, attitude (orientation of spacecraft) control, and autonomy systems are configured for the main thruster—440-Newton LAM—firing.
At 06:56:32 (T-21 minutes), forward rotation of the spacecraft starts, turning the spacecraft 180 degrees.
At 07:12:19 (T-5 minutes 13 seconds), eclipse starts.
At 07:14:32 (T-3 minutes), eight already-firing 22-Newton thrusters in the control system orient the spacecraft.
The spacecraft is currently moving at 22.57 km per second. In order to slow it down sufficiently so that it can be manoeuvred into the designated orbit (which is 423 km×80,000 km, according to ISRO), the main thruster, LAM, begins firing (known as “burn”), at 07:17:32.
Since the spacecraft is already rotated 180 degrees, the exhaust gases coming out of it oppose the motion of the spacecraft, thus slowing it down. In other words, they will decelerate the spacecraft. According to mission engineers’ calculations, the decelaration required is 1.1 km per second.
The burn continues for 1,454 seconds (24 minutes and 14 seconds), consuming 249.5 kg of propellant, and imparting incremental velocity of 1098.7 m/s.
The spacecraft is later reversed.
The interval between the start of the LAM burn and receiving the information about total burn performance is a kind of “tighter breathing and zero at the bone” time interval that could rip their personal space-time. To add to it, there will be Mars occultation during that time interval for a short span—when one object is hidden by another. The spacecraft will remain behind Mars and nobody can see it till the spacecraft emerges after brief period.
“It’s a do-or-die situation,” says Dr Shivakumar. He is the director of ISRO Satellite Centre (ISAC), a place where satellites are conceptualised, designed, built, tested, and commissioned. “We have more or less reached Mars, and with the orbital manoeuvre, we’ll finally be there.”
This is the first time we’ve gone such a long distance, he says. “This will show where ISRO is technologically placed.”
Exposed to the world of space missions, with “the world watching” and utterly alone as they navigate and guide the spacecraft over millions of kilometres to Mars—the team is a combination of vulnerability and strength.
The spacecraft has so far exceeded their expectations. Out of four planned mid-course corrections (December 2013, and April, August, and September of this year), one wasn’t necessary.
“We’re doing everything to make it a success. With the help of eight 22-Newton thrusters and the 444-Newton LAM (a total of nine thrusters), we should be able to give the right velocity—reduce the speed, basically—so that our satellite becomes the satellite of Mars,” says Shivakumar.
To make sure that the LAM is ready for use at 07:17:32, September 24, a test firing has been scheduled for September 22 (T- 41 hours), the day the spacecraft will enter Mars’ sphere of influence. Used way back on December 1 to send the spacecraft out of the earth’s orbit, the LAM has been dormant for more than 290 days. Complications such as corrosion can occur in fuel lines and propellant may not flow.
The procedure involves, Shivakumar explains, “opening two pyro valves onboard the satellite to make sure the fuel and oxygen is available to the LAM.” The LAM can then start firing. Starting at 14.30 hours, India time, and lasting 3.968 seconds, the test fire consumes 0.567 kg of propellant and imparts incremental velocity of 2.142 m/s to the spacecraft. The deviation of altitude caused by the test fire is around 200 km, from an estimated arrival altitude pre-test 723 km to post-test 515 km. The procedure is a part of fourth Trajectory Correction Manoeuvre (TCM-4) ahead of Mars orbital insertion.
The test firing is to primarily wake up the LAM two days earlier so that it doesn’t act up on September 24. Once they know that it’s working, they will send a sequence of commands—around T-30 hours—related to trajectory, to the spacecraft from the control centre to prep it for correct arrival altitude and trajectory. When MOM reaches the periareion point—closest approach to Mars—it will then be manoeuvred for Mars Orbiter Insertion (MOI).
Inserted now, the spacecraft enters Mars SOI in hyperbolic arrival trajectory sometime in October 2014.
This test firing, plus the operational schedule on September 24, is what the mission people envision as nominal mode. If all goes well, it will be strong capture of the orbit.
In case the LAM lies comatose, then there’s a contingency mode. It involves using eight 22-Newton thrusters, and manoeuvring the spacecraft into some other orbit, and bringing it back later, which, in their parlance, is called weak capture. For any eventuality other than nominal mode, the commands dealing with contingency will be executed.
Since LAM stirred awake in a crucial burn for 4 seconds, that contingency mode won’t be necessary at all. ISRO confirmed the test firing of the MOM’s LAM and trajectory correction. LAM is now operationally ready for critical Mars Orbital Insertion (MOI) on September 24. With successful test firing of LAM, the insertion maneuver will be in nominal mode.
“Main Liquid Engine test firing on Mars orbiter spacecraft successful: We had perfect burn for 4 seconds as programmed. The trajectory has been corrected. Mars Orbiter Mission will now go ahead with the normal plan for Mars Orbit Insertion,” says ISRO.
When a spacecraft reaches that far, it’s difficult to manage and control from the ground. The obiter’s computer is programmed to make decisions, and days before manoeuvres, engineers send up a sequence of code to execute actions on the appointed days, taking into account the delay that occurs in sending the commands. All this is part of onboard autonomy so that the spacecraft is self-directing.
Having uplinked all the commands, and verified them, 10 and nine days before, respectively, Shivakumar says, “it’s ‘sit and watch’ on September 24.”
Waiting and watching is one thing the team has not done till now. Every aspect—design, building, launching, peripheral fussing over its movement—has consumed them.
Arunan’s words carry an urgent intent: “let’s do it fast”; “that’s good, keep going”; “the pressure is good.” His phone beeps often—“you have to bear with me,” he says—now from the communication team, now from the simulation team.
Arunan sits on his chair, a strapping man of over six feet, legs almost reaching the end of the desk, suggesting parameters, asking the person on the other end to get it done fast. With a lot riding on the mission, any snag or glitch makes your angina unstable. In addition, MOM is an emblem of national ambitions.
It’s not just the mission people who are involved. Unlike in past missions, the ISRO project team opened up its mission’s progress to the general public via Facebook and Twitter, drawing in technologists, lovers of space technology, students, and many more.
“We need to have the whole country with us,” says Shivakumar.
The opening up has shown how deeply interested people are in MOM. “We are surprised by their interest,” Arunan says, gesturing as if there is a wide swath of people in front of him. “Some have even come up with calculations of velocities and trajectories.”
Launching an interplanetary mission is an excruciatingly cogitated and calculated risk. “In aerospace, there’s no adventure,” he says, “you have to test everything, over and over, until the risk involved is nil or very minimal.”
The mission has taught Arunan many things, especially the value of testing, and then testing some more.
“If there’s anything I learned on this project, it is never compromise on tests. We have done our homework well. We have left nothing to chance.” His hands sweep, illustrating the satellite’s trajectory. “In sending the spacecraft, we played to our genius.”
That genius is built as much on repetition as on creativity. Arunan says they tested the LAM engine with five different pieces of hardware to get good data. “You cannot satisfy yourself with just one test, with one piece of hardware. You need many tests to plot the data and establish a scatter of data.”
The spacecraft is configured on flight-proven IRS, INSAT, and Chandrayaan-1 bus systems. Additional modifications were done on power, communication, and propulsion systems, especially that of LAM. Since it’s very difficult to guide and navigate the spacecraft when it reaches the far reaches of space, onboard autonomy becomes crucial. The flight so far has validated the onboard autonomy. In fact, establishing the autonomy onboard is a technological leap for ISRO engineers who have been architects of an interplanetary mission for the first time.
(G B S N P Varma is a freelance journalist based in Andhra Pradesh.)
This story was updated on September 22.
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