Wednesday, October 22, 2008

Real science: Chandrayaan-I: Trajectory, similarity with a Fredric Brown story, & next steps

Related: More recent Chandrayaan updates are available.

Today morning, the first spacecraft from India for a mission beyond earth's orbit took off for a 2 year orbiting job around moon - "to provide a detailed map of the mineral, chemical and topographical characteristics of the moon's surface".

I'll restrict this post to what is not said elsewhere - or, at least, not emphasized. For information on mission: There are any number of news reports on the subject on pretty much any India-centric news service, & a Google search on "Chandrayaan" 4 hours after the launch threw up a quarter million documents, not counting those on Google News.

Trajectory: some education for me.

I got some education on trajectory of moon travel - it's a very complicated, rather than a near straight line or a simple curve.

Both Heinlein's "Moon is a Harsh Mistress" & Arthur Clarke's "Maelstrom II" gave the impression of some sort of straight flight - you blast off from one at escape velocity or may be a bit more in a certain direction, & eventually enter orbit or fall down the other. May be I was not paying attention. And I never looked up the trajectories taken by previous moon missions by other countries.

Here are quotes on Chandrayaan-I trajectory "after separation ... from launch vehicle ... Expected 19 minutes after lift-off" from a data box on the front page of today's Indian Express newspaper, Bombay, Late City edition:
  1. "Will circle the earth in elliptical orbit. Will fire rockets at scheduled stages to go into progressively higher orbits until it reaches 386,000 km from the earth. Will take 11 days to go around the earth in this orbit."
  2. "In the second revolution in this elliptical orbit, spacecraft will slow down to get sucked into moon's gravitational field after which it will start orbiting."
  3. "Then begins stepwise lowering into lower & lower orbits until it reaches the targeted orbit of 100 km from the moon."
This report from Indian Express online edition has a slightly different version of trajectory parameters.

Schematic illustrating the trajectory of Chandrayaan-I spacecraft of ISRO to moon

Update 1: This picture of trajectory makes things clearer. Click image for original sized BBC picture.

3D trajectory - schematic - of Chandrayaan-1 spacecraft on its way to moon, from ISRO site

Update 2: Much better trajectory image from ISRO site. Click image to enlarge.

When in doubt, use brute force.

I'd read this advice in my early days of programming. Seems to apply to a lot of situations.

Once in target lunar orbit, the spacecraft throws down something called "Moon Impacter Probe (MIP)." Expectations from 30 kg MIP are similar to those from Mars impacter in Fredric Brown's "Earthmen Bearing Gifts" that brought doom to Martians, though Chandrayaan's is a much lower energy projectile & thrown from close range.

For Indian readers: some food for thought.

Today's Bombay edition of The Economic Times newspaper gives these cost figures for various moon missions, apparently adjusted to today's costs in US dollars:
  1. Chandrayaan-I (India) (2008) - $86m
  2. Chang'e (China) (2007) - $187m
  3. Kayuga (Japan) (2007) - $480m
  4. Apollo (NASA, US) - $135b (yes, billion)
  5. From elsewhere: "NASA's upcoming half-a-billion-dollar Lunar Reconnaissance Orbiter".
While it's a genuine occasion to celebrate, I think the chest thumping on how we are the cheapest is unwarranted:
  1. I don't think comparison with Apollo is fair. That was a pioneering project in days when much less was known about the subject. And we are talking unmanned launches. I find the $0.5b upcoming NASA project a better comparison point.
  2. It will be a fair comparison when we convert $86m to purchasing power parity (PPP) numbers for local content. A locally made product costing $1 in US will likely cost you Rs 7 in India for equivalent local product, when the exchange rate is may be Rs 50/$ 47/$! Assuming Chandrayaan had a lot of imported components, I would reckon the PPP cost would be no less than $86x4 = $344m. No so cheap.
  3. I guess Chinese number would also be higher, once you look at it from purchasing power parity angle.

What next?

"landing a rover on the moon in 2011". Apparently, the budget is already approved by parliament.

May not yet be time to give up on space travel as impractical.

Related older bit from Technology Review about ISRO's scamject-based reusable launch vehicle "Avatar", due demo flight next year: "Avatar could thus deliver a 500-to-1,000-kilogram payload into orbit for about $67 per kilogram... Current launch prices range from about $4,300 per kilogram via a Russian Proton launch to about $40,000 per kilogram via a Pegasus launch."

OK - Avatar is for low-earth orbit. But still, $67/kg is about $4000 to launch me, not counting the cost of life support, radiation shielding, etc. May be space is not quite a lost frontier. What could our great-grandchildren expect 100 years from now?

And we are still in government monopoly era in this sector. If experience since early 1990s is any indication, fun in India really begins once private players enter a sector. What was it that really limited private players in the US in this sector? Was it lack of ideas on how to make money off moon or just lack of interest?

What next?

  1. All Chandrayaan posts.
  2. All moon posts, including fiction set on moon. A-rated stories probably won't disappoint. For free fiction, search for "full text" (without quotes). Or browse through all free fiction posts, including stories unrelated to moon.
  3. Subscribe to Variety SF master feed, Chandrayaan feed, or moon posts feed.