# India's Chandrayaan-2 and Vikram lander split amicably above Moon, SpaceX hops over Texas

As NASA nervously eyed Hurricane Dorian, Roscosmos finally persuaded Soyuz MS-14 to dock with the ISS and India's Chandrayaan-2 enjoyed an amicable separation above the Moon. India: Ready for powered descent? Following a sequence of successful manoeuvres in Lunar orbit, India's Vikram lander earlier today separated from the …

1. The lander is in an orbit of 119km x 127km and has a few more engine firings to go. A first deorbit burn is planned for tomorrow, taking the orbit down to 109km x 120km. A second manoeuvre on 4 September will send the lander to 36km x 110km.

Can someone explain these numbers to me? This looks like a distance being recorded as an area. What am I missing?

1. #### Apogee & Perigee?

(Furthest distance from surface/nearest distance from surface in irregular orbit)

1. #### Re: Apogee & Perigee?

Shouldn't that be; apoLun and periLun? Or apoapsis & periapsis

/Icon is the result of getting it worng :)

Ta!

2. #### Orbit numbers

Orbits are elliptical. These numbers are the highest and lowest points above the Moon's surface reached by the lander during one orbit, giving an idea of how eccentric the orbit is. The numbers given show that the lander is currently in a nearly circular orbit and will go into a lower orbit followed by an even lower and also less circular orbit.

Bear in mind that the actual orbit is around the barycentre of the two bodies and so they're all fairly close to being circular, but I suspect that height above ground is more useful for purposes which involve not attempting to orbit through a solid body ;-)

1. #### Re: Orbit numbers

Bear in mind that the actual orbit is around the barycentre of the two bodies and so they're all fairly close to being circular

Err, given that the moon outweighs the spacecraft by a factor of 10^20, for all purposes the barycenter of the bodies IS the center of the moon, you wouldn't need that to assess the eccentricity of orbits. Besides, my calculations give an eccentricity of 0.28 for the final phase orbit (110x36), which is not what I call close to circular.

1. #### Re: Orbit numbers

Besides, my calculations give an eccentricity of 0.28 for the final phase orbit (110x36), which is not what I call close to circular.

OK, mentioning the barycentre was a bit of a distraction :-)

As for eccentricity, what I was getting at is that "110 x 36" uses height above ground, which at this scale is more useful than the actual orbital parameters, which are measured between the centres of mass of the two bodies. So periapsis is not 36km, it's ((very nearly) radius of moon) + 36km = 1736 + 36 = 1772km; apoapsis is 1736 + 110 = 1846km; and using the calculation here the eccentricity is 0.02, which I class as close to circular (for which e = 0). I'm not sure how you got 0.28.

1. #### Re: Orbit numbers

My bad. I used this formula, considering the center of the moon as center of the ellipse instead of a focus. So I mixed up periapsis/apoapsis with semi-minor/major axis. Your figure is correct.

3. [quote]

Can someone explain these numbers to me? This looks like a distance being recorded as an area. What am I missing?

[/quote]

Basically all orbits are ellipses.

https://en.wikipedia.org/wiki/Elliptic_orbit

2. #### Exciting times

Russia gets the doors working, India is orbiting and Europe is torturing a rover.

Fingers crossed it all works out for the people involved.

I can't help but wonder though what will happen to the UK involvement after this exit farce finally concludes :(

1. #### Re: Exciting times

The Beeb's Sky at Night the other week did a special on mission selection for the European Space Agency and it looks from that program that the ESA are still on speaking terms with UK based space scientists.

1. #### Re: Exciting times

Though Brexit might well stimulate parts of the EU to reproduce the UK’s space industry* and do it for themselves. This might be induced by increased costs in moving things and parts about as the UK becomes a third country.

*Excepting the Glasgow satellite construction industry assuming Scotgov gets its a into gear and lets us have indyref2 in some form or other. Perhaps the rUK space bods will simply relocate to iScotland’s gain.

3. #### MS-14 booster is digital

The MS-14 Soyuz 2.1 booster is the first to have a digital flight computer. That's why it can do the azimuth roll, instead of having to be manually aligned on the pad.

4. #### Congratulations India

Well done. They have some decent rocketry and smart brains, despite the lack of NASA level resources. More countries should use Indian launches for their Satellites. Much cheaper and reliable. Would help all economies and boost for space science.

IIRC, they sent a Satellite to Mars for ONLY \$74 million. couple of years ago. Less then a Hollywood budget film.

They also carried US instruments in detecting water!

1. #### Re: Congratulations India

Seconded and they are doing useful stuff as well, not just indulging in national feel good stunts. They also seem to have at least as good a record on failures as good as everyone else despite their excellent thrift. I wonder if the Chinese are watching and learning.

5. #### One Lunar Day?

I'm sure the astorboffins in India had their reasons, but can someone point me to an article which explains why they didn't decide to add a bit extra (battery?) to keep everything alive but in hibernation during the night. Would they have had to upgrade all the instruments with insulation or something?

1. #### Re: One Lunar Day?

Temperature. The Chinese lander and rover use radio-isotope heaters to keep warm overnight, along with more insulation. It's all weight and the main purpose of this mission is just to land successfully and prove the technology. Expect longer surface life next time.

2. #### Re: One Lunar Day?

As Vulch said, it's all about thermal management. Lunar nights (because they are so long) are very cold. While the electronics themselves don't mind, most batteries can't survive such low temperatures, meaning that as the sun rises again there's no longer a power buffer available for things that take a lot of energy in a short burst (like transmitting data). While the craft might not be completely dead, effectively it is.

Due to the length of the night just adding more insulation isn't enough to keep things warm, you really need a heater. Spacecraft design is always a balancing act of vehicle weight versus the power available from the launch vehicle and decent stage. In this case they probably decided more instruments outweighed the benefit of extended mission time.

1. #### Re: One Lunar Day?

Yes, some claim mink fur is very warm but a dead mink in the cold is not warm at all.

3. #### Re: One Lunar Day?

It is part of the set of experiments . They have published several research studies on the ability to wake up the systems after the cold soak of a lunar night , including technical analysis of the Li-Ion cells being used at ultra low temperatures . There’s a greater than 0 chance that the systems will actually revive as they hope it will .

6. #### Back in the day

Man I really hope these guys have been practicing in their simulator first...

http://moonlander.seb.ly/

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