Starship development and progress [previous title: Will Musk's starship reach orbit this year?]

Miscellaneous and Personal Stuff I Must Share
1221

The article brings up a number of disparate concerns but doesn’t do a great job distinguishing between them.

As it directly relates to this thread, Starship will be a significant improvement to the current state of the art. First and foremost, it will fully reusable. Most rockets are not reusable at all. SpaceX’s Falcon 9 is partially reusable, but the second stage still burns up in the atmosphere (usually). Starship does not burn up at all.

There is also the question of propellant. The Falcon 9 uses kerosene and liquid oxygen, which does produce soot. It’s relatively clean compared to some others–for instance, solid rocket boosters generally have aluminum in the exhaust. And some other propellants are toxic. But still, it would be good to reduce soot. Starship uses liquid methane as fuel and due to it being a simpler hydrocarbon, produces almost no soot compared to kerosene. So it will be a significant improvement in that regard as well.

So on the launch side we’re seeing only improvements. But there is a legitimate question: by reducing launch costs so much, we’ll enable far more satellites to go up, and will those cause damage? That’s a definite maybe, but it’s far from clear yet. And there are things that can be done.

I’d say that aluminum is the main question here. It is by far the bulk of the satellite bodies and is designed to burn up in the atmosphere. That’s generally considered a good thing: it shouldn’t reach the ground, and it should also not stay in space forever. SpaceX has been a good steward in this respect, pushing for shorter lifetimes and lower orbits (which will naturally deorbit satellites faster). But that does have the side effect of putting more aluminum in to the atmosphere.

Space dust already deposits tens of thousands of tons of metals and other materials into the atmosphere per year. Even with a large increase in the number of satellites, they’re a relative drop in the bucket in terms of total materials. But for aluminum specifically, it’s relatively rare in space dust and so the quantity from satellites might have an outsized effect.

Satellite makers could start using more steel in their structures. That has some downsides and you’d have to do something like “glue” smaller segments together with lower melting-point materials (like aluminum) so that they separate on reentry and fully “demise”. But one can imagine reducing the aluminum quantity by 90% or something, at the expense of a bit more mass. There are some other possibilities like carbon fiber, though that’s more expensive. Some experimentation is in order. Japan made a wood-framed satellite, though I doubt that’s very practical in general.

Given that SpaceX has been very proactive in reducing light pollution from their satellites, and working with radio astronomers to minimize interference, not to mention their work on reusability, I think they’re likely to be fairly proactive here if the problems become more clear-cut. For now the science seems a bit speculative. They don’t seem to have any actual evidence of damage.

The Chinese are of course a different story and seem much less concerned about being good stewards. But that’s probably a subject for a different thread.

1222

Well, I did say through Earth’s atmosphere… :wink:
But true, aerobraking is obviously important for a Mars landing.
Though I suspect designing for that will be rather different from terrestrial re-entry?

In fact given the diversity of use cases, we can probably expect to see quite a number of ship variants eventually.

1223

I whish I could share your optimism:
https://www.nature.com/articles/d41586-024-02841-4

The huge explosions that destroyed SpaceX’s Starship mega-rocket last year also blew one of the biggest ‘holes’ ever detected in the ionosphere, a layer of thin air in the upper atmosphere. The hole stretched for thousands of kilometres and persisted for nearly an hour, a study found

1224

You’re right, of course: it has to be kept cold. The vapor pressure of oxygen or methane will go up very rapidly above the nominal boiling point.

Doesn’t sound very practical, at first glance anyway? The equipment would add non-payload mass. And then you have to get rid of the heat from the refrigeration cycle, and the only way to do that in vacuum is radiation. Ergo big radiator fins: more mass and probably awkward to deploy?

1225

My understand was that the perchlorate oxidizer that solid rockets use is absolutely terrible for the ozone hole. Has anyone addressed this?

1226

Presumably that’s because of the chlorine component?
Solid fuel boosters are a terrible idea, anyway.

As for aluminum… it’s the 3rd most common element in the Earth’s crust, so we’re hardly adding something exotic… presumably it mostly ends up as alumina (Al2O3) which is a common mineral.
Not saying that’s a GOOD thing to be scattering into the atmosphere, but I wouldn’t be surprised if volcanos emit orders of magnitude more than space activities?

1227

While Mars does have an atmosphere (I’ve heard it described as thick enough to be problematic, but not thick enough to be useful), it’s still a very different atmosphere from Earth’s, and so one would expect that the optimum design for Mars reentry would be very different from the optimum design for Earth reentry. If you even use aerodynamic control surfaces on Mars at all (which is not a given), they’re sure to be different sizes and shapes. The lower gravity on Mars would also, of course, be relevant.

You might not use a different design for the Moon, though. Conditions on the Moon are even more different from Earth than conditions on Mars are (no atmosphere, and even lower gravity), but they’re different in a way that makes everything much easier, such that almost any design could work well. At that point, the savings from using a (relatively) off-the-shelf design might outweigh whatever benefits you’d gain from optimizing to the environment.

1228

Thinking about this some more, solid fuel boosters are almost always used as part of a first stage, and are jettisoned quite early in the ascent. So does any of their exhaust directly impact the altitude at which the ozone hole is an issue?
Of course there may be some atmospheric mixing, but my layman’s understanding of this is that there isn’t a lot of rapid mixing between the layers of the atmosphere… anyone with real knowledge please correct me…?

Getting a bit off topic from Starship (which wisely eschews solid boosters)… perhaps we should move this particular discussion into the ongoing space forum…?

1229

According to this YouTube video https://www.youtube.com/watch?v=z-XVAkmcmjw Mars aerobraking will require Starship to enter Mar’s atmosphere inverted, to produce negative lift. The reason being so that it can follow the sharper curve of Mar’s upper atmosphere long enough to slow down without excessive heating or g-forces. Otherwise at interplanetary transit speeds it would overshoot Mars and skip back out into space.

1230

It’s still a test program. And they haven’t exploded any vehicles in the upper atmosphere in a while. The latest flights have done something no other rocket has–go up and come back down without disposing of anything in the atmosphere. Even the semi-reusable Shuttle sent its large external tank to burn up on re-entry.

1231

It’s definitely not a trivial problem. I wouldn’t expect it on HLS. But the depot, maybe. It just stays in LEO and can afford some extra mass since it’s not going anywhere. If the depot is intended to be a long-term thing, it probably makes sense to add the required equipment. Among other things, it means that if there’s a delay on the HLS side, the depot can just hang out indefinitely even when filled.

1232

Well I fear it is not a good situation, but I appreciate it is getting better. That is something. And I agree with your post where you say that the Chinese program (and the Indian one, or the Russian, whatever is left of that one) cares much less for the environment, but that is a small consolation. A program that is ten times better but launches 50 times more rockets is not better in the end.

1233

The Chinese are at least still interested in cost effectiveness. So they’re working on methane propellant and reusable rockets as well (in fact a small Chinese company was the first to reach orbit on a methane rocket). They may not care about the pollution per-se, but pollution is waste, and waste costs money.

India’s program is too small to be much of an effect, and Russia is quickly going defunct. Europe’s new Ariane 6 is not good–totally non-reusable, and depends on those solid boosters that dump chlorine into the upper stratosphere. But it’s not going to fly very often due to the high cost (it’s basically a make-work program to keep solid-rocket tech expertise in Europe).

I’m not going to say that everything’s perfect–the new space race will undoubtedly exacerbate some old problems and uncover new ones–but at the same time, the new capabilities mean we have much better means of dealing with those problems.

As an example of this, most rockets use helium to pressurize their tanks. Helium is a non-renewable resource that’s critical for medical and other uses. Starship would need extreme, unsustainable amounts–so instead, they switched to autogenous pressurization, basically pressurizing the liquid methane tank with methane gas, and the liquid oxygen tank with oxygen gas. No waste, no unsustainable resource use. Good for everyone.

1234

The only real answer to this charge is a radical shrinking of the populace and the per capita output of the economy and a radical de-teching of everything.

Imagine a time portal back to ~1600AD. That’s how we stop perturbing the planet’s ecology in unknown ways to unknowable results. Anything less is mere window dressing.

I can sorta barely get behind the idea of not adding the new problem of meso-atmospheric pollution to all of humanity’s other sins. Almost.

Then I remember how many hundred thousand tonnes of VOCs are released annually by dry cleaning plants doing our clothing. Or the total ecological impact of hunanity’s pets. The numbers are staggering.

We are already too much impact per person and too many people for our teeny little limited planet.

Choosing to curtail spaceflight when we find it too hard to insulate our homes amd businesses seems silly. And it remains too hard despite the fact home insulation has an ROI north of 20% per annum for the entire life of the building.

YMMV.

[Rant off] :wink:

1235

Thinking about this some more… while double-move of material is usually something to be avoided if possible, it probably does make sense to have one or more tankers permanently provisioned in orbit.

It decouples fuel transport from other missions, which should be good for flexibility of scheduling.

1236

However Starship is still expected to have to store cryogenic fuel for ~260 days so as to be able to land on Mars when it gets there (or on Earth at the return trip). So that’s got to be worked out somehow.

1237

I’d rework that to read

… store cryogenic fuel for ~260 days with an acceptable loss percentage so as to …

For big enough tanks, even a lot of loss still eaves enough for the mission at hand. Zero is not necessarily the goal.

1238

I would hope they are at least thinking about this?

At least at a level better than “No worries, we’ll just slap a bit of white paint on it. She’ll be right mate…”.

Of course I said something similar about re-entry a while ago, and they do seem to be addressing that. There are some competent engineers at SpaceX , I think…

1239

Remember they first developed Crew Dragon; different shielding technology to be sure, but it does mean that the people at SpaceX who design and build stuff have to be familiar with just what happens at hypersonic reentry speeds. The contrast with Boeing’s Orion is notable.

We’ve already had a couple of Starships reenter from near-orbital velocity and retain the fuel needed for a soft splashdown despite the heating they underwent. So I’m confident that at the least the SpaceX engineers are familiar with just how rapidly heat transfers from the outside of the rocket. So for long-term storage it’s a matter of reducing heat gain and/or increasing heat loss.

1240

A depot makes a lot of sense when you’re talking about refuelling a manned mission. You don’t want to have humans on board your ship while you dock to twenty different refuelling craft and hope that they all work right. Much better to dock those 20 to an unmanned depot, and then if some don’t work right, launch a few more, and then only launch the humans once you’re sure the depot is filled.