ISRO's announcement Announcement of Opportunity (AO) for future Mars Orbiter Mission (MOM-2) says in part:

It is now planned to have the next orbiter mission around Mars for a future launch opportunity. Proposals are solicited from interested scientists within India for experiments onboard an orbiter mission around Mars (MOM-2), to address relevant scientific problems and topics.

This “Announcement of Opportunity (AO)” is addressed to all institutions in India currently involved in planetary exploration studies / the development of science instruments for space. This orbiter mission will facilitate scientific community to address the open science problems. The Principal Investigator of the proposal should be (i) able to provide necessary details of the instrument which can address the scientific problems and (ii) capable to bring together the instrument team and lead the team for developing a space qualified instrument.

The payload capability of the proposed satellite is likely to be 100kg and 100W. However final values are to be tuned based on the final configuration. The apoarion of the orbit is expected to be around 5000 km. (emphasis added)

I can udnerstand that things like the estimated mass (~100 kg) can be specified as they are highly dependent on the launch vehicle's capability. Stating the power estimate of ~100 W suggests to me that the spacecraft's bus will be managed by ISRO and they are budgeting roughly 100 W to support the experimental payload.

However I can't venture a guess why the apoarion (apoapsis of the Mars orbit) has been chosen to be around 5,000 km, and why a lower, circular orbit has been excluded for at least part of the mission.

Question: Why would ISRO's MOM-2 Mars orbiter mission's apoarion already be decided in such an early call for proposals?

  • $\begingroup$ because that informs decisions on sensors (lens specs for cameras, etc.) $\endgroup$ – Hobbes Jul 22 '18 at 7:23
  • $\begingroup$ @Hobbes the body of the question why it "has been chosen". I've changed "specified" to "decided". I'm not asking why the apoarian was made available as that is darn obvious. I'm asking why the apoarian has already been decided. $\endgroup$ – uhoh Jul 22 '18 at 7:37
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    $\begingroup$ I hesitate to write an answer, as only ISRO can do that. Most likely scenario - lower orbits take more propellant for insertion. They may not have sufficient propellant to bring the orbit any lower. (MOM 1 has an orbit of 80000x420 km so 5000 would be a huge improvement). Other possibilities: To expand @hobbes point - they may already have a particular science mission in mind which in turn drives an apoapsis. Higher apoapsis also reduces eclipse length, which can reduce battery and solar array size. $\endgroup$ – Carlos N Jul 23 '18 at 3:14
  • $\begingroup$ @CarlosN I didn't realize that MOM 1 had such an extreme orbit, wow! Yes this would be a big improvement. I think there's nothing wrong with posting a answer like that if it is supported with one or two links. $\endgroup$ – uhoh Jul 23 '18 at 3:21

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