# Please explain the physics of a spacecraft launching from the Moon or from Mars **URL:** \ **Category:** Factual Questions\ **Created:** [August 27, 2020, 10:23pm UTC](https://boards.straightdope.com/t/please-explain-the-physics-of-a-spacecraft-launching-from-the-moon-or-from-mars/919189 "2020-08-27T22:23:35Z")\ **Posts on this page:** 10\ **Page:** 6
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 3, 2021, 11:59pm UTC](https://boards.straightdope.com/t/please-explain-the-physics-of-a-spacecraft-launching-from-the-moon-or-from-mars/919189/101 "2021-01-03T23:59:16Z")
> [@Dr.Strangelove](#): > > Another consideration here is that the Tesla Cybertruck will need enormous amounts of stainless. The gauge and alloys will be different, and of course Tesla is a different company from SpaceX, but the volume from that may give Musk a bit of extra clout with prospective suppliers. It occurs to me that a truck is not nearly as demanding as a spaceship, and could probably tolerate a wide variety of steels. Might Musk be planning on finding just the right alloy for spaceships, and then using whatever that alloy is for trucks as well to get the needed economies of scale? ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [January 4, 2021, 12:24am UTC](https://boards.straightdope.com/t/please-explain-the-physics-of-a-spacecraft-launching-from-the-moon-or-from-mars/919189/102 "2021-01-04T00:24:54Z")
> [@Stranger\_On\_A\_Train](#): > > but Elon Musk is notorious for underestimating delivery on schedule, often by years He’s often better at longer-term predictions than the shorter ones. He predicted Tesla producing a half-million cars by 2020 [back in 2014](https://www.tesmanian.com/blogs/tesmanian-blog/tesla-on-tracks-to-produce-delivery-500k-units-as-elon-musk-predicted-in-2014#:~:text=But%20despite%20naysayers%2C%20Musk%20in,cars%20a%20year%20by%202020.%E2%80%9D), and they just hit that number. Not without some chaos in the interim, of course. And he’s ok at predicting clearly-defined outcomes, like the on-time construction of the Hornsdale Power Reserve or Gigafactory Shanghai. Just take his predictions on full self-driving with a grain of salt 🙂. Starship development is making concrete progress at any rate. I’m not counting on them hitting any particular date, just continuing to make rapid progress. > [@Stranger\_On\_A\_Train](#): > > Musk’s ventures of SpaceX and Tesla have enormous valuations, of course, but those literally incredible numbers are a house of cards; Tesla couldn’t make the profit to justify its current valuation in decades of even high volume production, and while the profitability of SpaceX is unknown to the public it cannot be nearly enough to cover this effort Maybe so, but both companies have been able to convert their crazy valuations into hard cash without crashing. Starlink, once it’s fully up and running, should be a cash cow and easily exceed SpaceX launch revenue, at least in the short term. It’ll likely justify Starship develop all by itself just to maintain the constellation. I think the rapturous demand will come eventually, but will take some years for people to really wrap their head around. For the price of the James Webb scope, we could have a huge constellation of space telescopes, designed to be cheap and robust, not like delicate origami. A similar idea with NASA’s planetary exploration–take mass and price out of the picture, and you can totally change how you design probes and landers. But it’ll take a long time for those lessons to sink in. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [January 4, 2021, 12:30am UTC](https://boards.straightdope.com/t/please-explain-the-physics-of-a-spacecraft-launching-from-the-moon-or-from-mars/919189/103 "2021-01-04T00:30:11Z")
> [@Chronos](#): > > Might Musk be planning on finding just the right alloy for spaceships, and then using whatever that alloy is for trucks as well to get the needed economies of scale? Certainly a possibility. Musk has said the alloy will be the same, though that feels like the kind of thing that could easily change. The requirements are different, of course–the Cybertruck doesn’t need to work at cryo temps, for instance–but if they hit on something with good fabrication properties (weldability, machinability, etc.), it might be worth the commonality. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [January 4, 2021, 1:06am UTC](https://boards.straightdope.com/t/please-explain-the-physics-of-a-spacecraft-launching-from-the-moon-or-from-mars/919189/104 "2021-01-04T01:06:44Z")
> [@Chronos](#): > > It occurs to me that a truck is not nearly as demanding as a spaceship, and could probably tolerate a wide variety of steels. Might Musk be planning on finding just the right alloy for spaceships, and then using whatever that alloy is for trucks as well to get the needed economies of scale? It is not an issue of one application being “more demanding”; it is a question of selecting the correct material for the application that balances physical properties like strength and corrosion resistance, manufacturability, and cost. A steel for making automobile chassis and bodies needs to be highly formable and easily welded without preparation or preheating, hence why no production automobile (that I’m aware of) has been made with a stainless steel chassis despite the obvious advantage to corrosion resistance. It does not need to survive cryogenic temperatures, high temperature creep, or ablation due to ionization. It would make little sense to spend $10/kg for an aerospace grade low carbon high temperature service alloy for a car chassis to achieve any economy of scale when a $2/kg corrosion resistant high carbon steel with good formability and ready weldability is available. > [@Dr.Strangelove](#): > > Starlink, once it’s fully up and running, should be a cash cow and easily exceed SpaceX launch revenue, at least in the short term. It’ll likely justify Starship develop all by itself just to maintain the constellation. Yeah, that is what a number of satcom companies have believed over the years: [_Wired_: “SpaceX Is Banking On Satellite Internet. Maybe Ot Shouldn’t.”](https://www.wired.com/story/spacex-starlink-satellite-internet/). Satcom is a tricky business that few companies have actually made consistent profit without government subsidy, notwithstanding how this giant fleet of small satellites in Low Earth Orbit is going to fuck with ground-based astronomy and pose a potential threat of a Kessler Syndrome-type although at least the V-band satellites are in a low enough orbit that they’ll decay in a few years. All it would take to undercut Starlink would be for Charter to get backing to lay fiber optic cable to every small town and cell companies to actually deploy ground-based 5G service everywhere, and the demand for high speed satellite internet service declines to the developing world and poor New Zealand that can’t convince a yone to lay another underwater trunk line so they can stream Youtube like everyone else. There are certainly other opportunities in superheavy lift but there isn’t much market for it now even if it were dirt cheap, and putting up space telescopes for academic use as fast as they can be funded and built is a sustainable business model. There are more plausible models like freefall manufacture but it isn’t as if anyone is chomping at the bit awaiting the capability, and most the products once hypothesized to require freefall conditions have been produced on Earth with improvements in manufacturing technologies. Stranger ---
**Author:** ![Euphonious\_Polemic](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/euphonious_polemic/32/3002_2.png) [@Euphonious\_Polemic](https://boards.straightdope.com/u/Euphonious_Polemic)\ **Post date:** [January 4, 2021, 1:56am UTC](https://boards.straightdope.com/t/please-explain-the-physics-of-a-spacecraft-launching-from-the-moon-or-from-mars/919189/105 "2021-01-04T01:56:00Z")
> [@gnarator](#): > > That’s really good. Sadly, Estes doesn’t seem to make the E9-4 anymore… They make an E16-4, which is much more useful. ---
**Author:** ![gnarator](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gnarator/32/8266_2.png) [@gnarator](https://boards.straightdope.com/u/gnarator)\ **Post date:** [January 4, 2021, 2:08am UTC](https://boards.straightdope.com/t/please-explain-the-physics-of-a-spacecraft-launching-from-the-moon-or-from-mars/919189/106 "2021-01-04T02:08:30Z")
That’s a 29mm motor, not a 24mm motor. They still have the E12. I liked the long burn on the E9. I’ve had bad luck with CATOs on E12s, but my E9s flew great. Others report the opposite. ---
**Author:** ![Euphonious\_Polemic](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/euphonious_polemic/32/3002_2.png) [@Euphonious\_Polemic](https://boards.straightdope.com/u/Euphonious_Polemic)\ **Post date:** [January 4, 2021, 2:25am UTC](https://boards.straightdope.com/t/please-explain-the-physics-of-a-spacecraft-launching-from-the-moon-or-from-mars/919189/107 "2021-01-04T02:25:24Z")
Personally I like a composite E30. Gets up and goes! ---
**Author:** ![gnarator](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gnarator/32/8266_2.png) [@gnarator](https://boards.straightdope.com/u/gnarator)\ **Post date:** [January 4, 2021, 2:28am UTC](https://boards.straightdope.com/t/please-explain-the-physics-of-a-spacecraft-launching-from-the-moon-or-from-mars/919189/108 "2021-01-04T02:28:54Z")
I like the E15/E20, E30, and F44, but I’ve had trouble with getting the delays right for rockets that take an E9-4. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [January 4, 2021, 11:36pm UTC](https://boards.straightdope.com/t/please-explain-the-physics-of-a-spacecraft-launching-from-the-moon-or-from-mars/919189/109 "2021-01-04T23:36:55Z")
> [@Stranger\_On\_A\_Train](#): > > All it would take to undercut Starlink would be for Charter to get backing to lay fiber optic cable to every small town and cell companies to actually deploy ground-based 5G service everywhere Sure. But we already have an answer here, in the form of the FCC subsidy auction: > **[SpaceX gets $886 million from FCC to subsidize Starlink in 35 states](https://arstechnica.com/tech-policy/2020/12/spacex-gets-886-million-from-fcc-to-subsidize-starlink-in-35-states/)** > > Charter also wins big; FCC fund will bring service to 5.2M homes and businesses. And yeah, Charter did get a chunk of change to run fiber to underserved areas. But SpaceX got a decent award as well. The auction could have been run a bit better but overall seemed to serve its purpose, and successfully pit providers against each other to provide service level X for price Y. Those values differ between technologies; running fiber to buttfuck nowhere isn’t economical, and neither is using satellites to serve dense urban areas. The auction seemed to do a reasonable job in giving subsidies to the provider with the most appropriate technology for the area. There’s a second phase coming up with another $11B at stake. I don’t see the outcome being too different from the first phase, though. It’s true that satellite constellations don’t have a great history (Musk himself said “We just want to be in the ‘not bankrupt’ category, that’s our goal”). But then, no one else had a marginal launch cost of ~$15M, nor tried packing in 60 satellites per launch, or _really_ cost-optimized those satellites, or took significant advantage of ridesharing. ---
**Author:** ![3AxisCtrl](https://avatars.discourse-cdn.com/v4/letter/3/ecd19e/32.png) [@3AxisCtrl](https://boards.straightdope.com/u/3AxisCtrl)\ **Post date:** [January 8, 2021, 12:47am UTC](https://boards.straightdope.com/t/please-explain-the-physics-of-a-spacecraft-launching-from-the-moon-or-from-mars/919189/110 "2021-01-08T00:47:48Z")
> [@Stranger\_On\_A\_Train](#): > > Stainless steel, like most metals, is very thermally conductive … It’s actually quite low on the scale of thermal conductivity - for metals. Which of course does not mean it entirely avoids the thermal energy transfer problem you note. But this may increase its appeal here. [Previous page](https://boards.straightdope.com/t/please-explain-the-physics-of-a-spacecraft-launching-from-the-moon-or-from-mars/919189.md?page=5)