#Chandrayaan2 – the space-exploring, moon-landing, lunar-roving flying machine that Indians in 5019 AD will call 'ancient pushpak vimanas' and actually be right for once – is set to lift off onboard a #GSLVMkIII rocket at 2.51 am on July 15, on the rocket's M1 mission. 1/n
There is a tremendous amount of details surrounding this one mission, with good reason: it's India's most complex robotic mission to date. A #PSLV launching a hundred satellites into different orbits pales compared to what's going on here. E.g., the rocket itself 2/n
has been fit with the new CE20 cryogenic engine, whose development began in 2002 and which completed its integration full-duration hot test in 2017. isro.gov.in/update/26-jan-… Though it's one of the most powerful such engines in the world, many people seem to think 3/n
that makes the #MkIII a very powerful rocket. It's not. It's a medium-lift launch vehicle. There's the heavy-lift class above it – the sort of vehicle we'll need if we're going to regularly undertake human spaceflight and lunar payload missions. Note here that the Falcon 9 4/n
costs as much as the Mk III but can carry a heavier payload, so ISRO's cost-cutting has a way to go. After the engine, there's the payload itself. The 3,877-kg stack called #Chandrayaan2 is an assemblage of three units: an orbiter, a lander and a rover. 5/n
The last two are called #Vikram & #Pragyan, resp. This is the mission sequence (per ISRO): thewire.in/space/isro-cha…

An interesting point: the CE20 engine in the C25 cryogenic upper stage also flew on the Mk III D2 mission, which launched the GSAT-29 satellite in November 2018 6/n
GSAT-29 weighs 3,423 kg and was injected into a slightly less elliptical orbit than #Chandrayaan2 will be. However, a comparison of the two (planned) mission profiles shows the engine burns to be of slightly lesser durations on the Mk III M1 mission. This means upgrades 7/n
But what upgrades I don't know: public.flourish.studio/visualisation/… (link to interactive version) 8/n
.@uncertainquark wrote a comprehensive article for @TheWireScience about the specifics of this mission (plus some trivia!). Load it up and you'll know almost everything there is to know about this mission on a single screen, broken down step by step: thewire.in/space/chandray… 9/n
Some additional details: on bioastronautics neurologyindia.com/article.asp?is…
About the 800 N engines researchgate.net/publication/29…
Review of potential landing sites web.archive.org/web/2018082205… 10/n
And no matter what anyone tells you, #Chandrayaan2 is NOT going to the Moon to look for helium-3. We've all got better things to do: rootprivileges.net/2019/07/13/fir… 11/n
.@Viratmarkandeya dug deeper into why the batteries are the principal limiting factors on this mission. Vikram/Pragyan will land at the dawn of a lunar day and do their thing. At dusk, their batteries will power down and hibernate for the night – but they might not wake up 12/n
Reason: the lunar night is so cold that batteries might not be able to warm up again: indianexpress.com/article/expres…
This illustrates the connection between fundamental research + its apparent uselessness on the one hand and applied science + its apparent superiority on the other 13/n
Neither position is entirely and absolutely correct but this hierarchy of priorities closely parallels the practices of the populist politics that privileges short-term gains over benefits in the longer run.
It may not seem worthwhile to fund a solid-state physicist who has, 14/n
based on detailed physicochemical analyses, fashioned e.g. a new carbon-based material that can store lithium ions in its atomic lattice and has better thermal characteristics than graphite. It may seem even less worthwhile to fund researchers probing the obscure 15/n
electronic properties of materials like graphene/silicene, writing papers steeped in abstract math and unable to propose a single viable application for the near-future. But give it 20 years and a measure of success in the otherwise-unpredictable translational research 16/n
part of R&D pipeline and suddenly, you’re holding the batteries to be installed on a Moon rover and need to determine how many instruments you can pack to ensure the whole ensemble is powered for the time they’ll need to conduct their tests (this bit from an older blog post) 17/n
.@sandygrains and @AGirlHasWords compiled an interesting 'Talk Point' about what gains we can expect from #Chandrayaan2: theprint.in/talk-point/isr… @somakrc makes an important point: that these interplanetary missions are important first-steps but he also reminds us 18/n
that they can't just be about national pride. Springboarding off his comments: #Chandrayaan2 can't, and shouldn't be allowed to, coast on the pride factor. As a science mission, it needs to deliver on the science and ISRO needs to be seen to be delivering it: 19/n
data in the public domain (no one-picture-per-week business), scientific papers, technical reports. Both MOM and #Chandrayaan1 have been relative flops on this front (e.g. old.reddit.com/r/ISRO/comment…) 20/n
Finally, @cosmosguru analysed a commercial prospect: "A comparison of the capacity that these companies are trying to establish with ISRO’s #Chandrayaan2 points to some early evidence that India’s space agency may be able to offer a better price-performance" 21/n
in terms of carrying payloads to the Moon theprint.in/science/as-the…
Here, M. Ramesh recalls the tense moments before #Chandrayaan1 lifted off in October 2008 thehindubusinessline.com/news/science/c… 22/n
(TL;DR: the oxidiser, a highly poisonous substance called nitrogen tetroxide, leaked through a fault in the connection between the oxidiser tank and a pipe, engulfing the rocket in a pink smoke that had to be cleared away asap before the fault could be fixed). 23/n
Let's hope nothing goes wrong tonight, but let's also remember to not be surprised if something does: the Mk III is much more complex as a rocket than the PSLV, and Moon landings themselves have had a historical success rate of around 50%. 24/n
Speaking of which: assuming today's lift-off mission will be a success, July 15 will be a historical date; the more significant thing will happen on September 6/7, when the lander will attempt to descend gently on the Moon and when (four hours later) the rover will roll out 25/n
Unlike what ISRO usually does, this is a longer duration multi-step mission with a lot that needs to go right (and a lot that can go wrong). I don't mean to be a downer but simply remembering we're far from done isn't exactly the same as declaring failure, 26/n
or even criticism for that matter. To rephrase what one space scientist told me: if lander fails, we must go back to the launchpad; if the rover fails, it's a smaller problem but we must still go back to the launchpad; 27/n
if the orbiter fails: "heavy space systems to the lunar surface are for practical reasons expected to be modular" so "the carrier modules need to be robust", so we'll likely to back to the launchpad; if the Mk III fails, "it's more worse in certain ways: … 28/n
if the capacity to launch remains similar or barely grows over time, all interplanetary missions would be limited."

Some important links:
ISRO livestream cdn.24fd.com/e19/07/isro/15… homepage isro.gov.in/chandrayaan2-h… kit isro.gov.in/gslv-mk-iii-m1… 29/n
June 13 ISRO presser about a third Moon mission unoosa.org/documents/pdf/…
A kind soul has set up a countdown for you to time yourself (in case you aren't one of those people at the new Launch View Gallery tonight): timeanddate.com/countdown/laun… 30/n
Btw, people in Chennai: you'll be able to watch the launch from your rooftops, although not in much detail unless you have a pair of binoculars or something better. And for any photographers out there: if you take good pics, please consider placing them in the public domain 31/n
(© terms of ISRO images are vague: thewire.in/space/ekta-kap…). I'd very much like to emblazon a good image on a tee for myself!

In all: enjoy the launch, keep asking/looking for more info at this important time, and know that there's as much info out there as fake news. 32/32
PS: tweet 29/n – correct link for mission homepage isro.gov.in/chandrayaan2-h…
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