New Mars Forums

You are correct that carbon fiber itself is stronger than steel. The problem is to form it into propellant tanks the individual fibers have to be epoxied together. It’s the epoxy, i.e., glue, which makes the structure weaker than the individual fibers. Carbon fiber tanks are more accurately called carbon-fiber composite tanks because they are a composite material containing the carbon fiber and the epoxy. Look up strengths of carbon fiber composite tanks.

  Bob Clark

Rereading that article by Andrew Parsonson. I think he is referring to the methane-fueled Ariane Next program, not a supposed all hydrolox-Vulcain engine version.

But interestingly, such a methane-fueled launcher might cost 50% that of the Ariane 6, and thus be competitive with the Falcon 9 prices. This is described here:

DOI: 10.13009/EUCASS2019-949
8TH EUROPEAN CONFERENCE FOR AERONAUTICS AND SPACE SCIENCES (EUCASS)
Ariane Next, a vision for a reusable cost efficient European rocket.
Antoine Patureau de Mirand*, Jean-Marc Bahu*, Eric Louaas*
*Centre National d'Etudes Spatiales (CNES), 52 rue Jacques Hillairet – 75612 Paris Cedex, France Corresponding Author (****@cnes.fr)


https://eucass.eu/index.php/component/d … d&id=5506…

This is the point I have been making. The large solid side boosters on the Ariane 5/6 are not price competitive. By switching to all liquid reusable engines you can get launchers price competitive to the Falcon 9.

  Bob Clark

ESA Publishes Call for Reusable Rocket Booster Concepts
By Andrew Parsonson - February 10, 2024
The phrasing of “liquid reusable booster” and the fact that the programme will potentially be aimed at existing launch systems suggests that this may be part of an Ariane 6 evolution. If this is not one of the direct aims of the initiative, ArianeGroup will certainly be in a position to utilize BEST! as a means to fund, at least partially, the transfer of the knowledge gained during the ongoing development of the reusable booster demonstrator Themis to an evolved Ariane 6 variant.
https://europeanspaceflight.com/esa-pub … -concepts/

This is great news for European space flight. I find it quite notable the author of this article on the new ESA push for reusability is asserting that it may involve an evolution of the Ariane 6. This is important, for if it is to be reusable then the solid SRB’s must be dispensed with. Now, it is possible such an evolution would involve the methane-fueled Prometheus engine. But in my opinion, using a completely different engine with even different propellant should not be regarded as an evolution of the Ariane 6. It would be an evolution of the Ariane 6 to reusability if using the same hydrogen-fueled Vulcain engines but not using the SRB’s.

Quite key for these new launcher developments is to follow the SpaceX model of private financing for the launchers. That way 90% of the development costs can be saved: a mid-sized orbital launcher can be developed for only a few hundred million development cost, not the billion dollars thought necessary when such launchers were government financed. See discussion here:

Towards Every European Country's Own Crewed Spaceflight, Page 2: saved costs and time using already developed, operational engines.
https://exoscientist.blogspot.com/2024/ … s-own.html

The key, and most controversial, points:

1.)Any European country can field their own, independent, manned flight capable launcher in under 2 years, IF they design it around already developed and operational engines.

2.)By eliminating the two SRB’s on the Ariane 6, and instead adding 1 or 2 additional Vulcain engines on the core stage, ArianeSpace can field such a launcher in less than a year.

3.)In any case, such a manned flight capable launcher by following the commercial space approach spear-headed by SpaceX could be developed for less than $200 million, assuming they didn’t have to pay engine development costs by using already operational engines.

  Bob Clark

Thanks for that. That sounds like it’s done after the mission is completed. Has it been done while the engines are still firing where the stage has not completed its portion of the flight?

  Bob Clark

I’m aware of that. My suggestion that the expendable payload size could be maintained even at 75% reduced thrust is coming from the idea the expendable stage dry mass can be greatly reduced from the dry mass of the stages now in the reusable versions.

It’s all dependent on this statement by Elon Musk:

Elon Musk @elonmusk
Probably no fairing either & just 3 Raptor Vacuum engines. Mass ratio of ~30 (1200 tons full, 40 tons empty) with Isp of 380. Then drop a few dozen modified Starlink satellites from empty engine bays with ~1600 Isp, MR 2. Spread out, see what’s there. Not impossible.
9:14 PM · Mar 29, 2019
https://x.com/elonmusk/status/1111798912141017089?s=20

That 40 ton dry mass Elon suggested there for the expendable Starship is 80 tons less than the cited reusable dry mass of 120 tons. 80 tons is a *huge* difference in dry mass, especially for an upper stage where every extra kilo subtracts directly from the payload that can be carried.

Presuming you also get a greatly reduced dry mass for the SuperHeavy results in such a high expendable payload even for Raptors running at 75% thrust.

  Bob Clark

This video attempts to argue the Raptor is reliable by looking at static fire tests:

1000 Starship Engine Tests (on a graph).
https://www.youtube.com/watch?v=I6GJVvwUEGk

A key question in the video is how many of the test fires fall short of the expected length, suggesting a test failure or for whatever reason the engine had to be shutdown. The video host suggests it is small number. I suggest it is more than it should be for an engine at this stage in its development. Someone may want to count the percentage themselves where it is displayed graphically at about the 5:55 point in the video.

Also I don’t like the lengths of the engine tests. The video host says most are about 2 minutes, 120 seconds, suggesting that is where SpaceX thinks that is what the flight burning time should be. But judging from the test flights for the booster that should be in the 2 minutes 40 seconds range, 160 seconds, https://en.m.wikipedia.org/wiki/SpaceX_ … ht_profile, which means even for static fires of individual engines SpaceX is not doing realistic static fires.

Additionally, SpaceX needs to be open about how many of these static fires are done at full power.

  Bob Clark

For every other rocket intended for orbital flight they do full up(all engines together), full thrust, full flight duration(several minutes long) static tests. But for both stages of the Superheavy/Staship all they do are these 50% thrust burns of only a few seconds duration.

Why? For the SuperHeavy booster with its 33 engines an explanation that has been offered is it’s “too big”. But that explanation doesn’t make sense for just the 6 Raptors on the Starship. So why hasn’t SpaceX done such flight simulation static burns, which are just standard industry procedure, even for the Starship?

The most obvious reason is SpaceX believes it would cause a RUD.

   Bob Clark

GW, you commented on my blog:

What I hear from the ground testing at the McGregor site (6 miles from my front porch) is no more Raptor starts at full power. I suspect they may have learned the hard way not to do that.

Do you mean by that the static tests sound like they are no longer doing full power tests or someone connected to SpaceX said they won’t?

  Bob Clark

Manned missions to Callisto at less than 2 year travel time using chemical propulsion only are explored by this author:

https://x.com/bellikozan/status/1718725 … 48101?s=61

  Bob Clark

SpaceX @SpaceX
Flight 3 Starship completed a full-duration static fire with all six of its Raptor engines.
Embedded video
0:11 5:40 PM · Dec 20, 2023·1.3M Views
https://twitter.com/SpaceX/status/17376 … 33181?s=20

I really dislike this phrasing of SpaceX of calling a burn “full duration” to mean it lasted the planned time of the burn, even if it was only 5 seconds. It used to be the term “full duration” meant the length of an actual flight burn, which will be several minutes long.

If you want to say the burn lasted the planned length just say it lasted the planned length.

It’s hard to believe that both the FAA and NASA would be effected by this “Jedi mind trick”: just call it “full duration” and that means the engines have been fully flight qualified for a full burn time in flight.

  Bob Clark

Two separate, independent methods suggest SpaceX throttled down the booster engines < 75%, while the Starship engines fired at ~90% thrust.

This is important to know because if the engines need to operate at < 75% to be reliable, then I estimate the reusable payload would be lowered from 150 tons to ~100 tons. Then instead of needing perhaps 16 refueling flights for the Artemis landing missions there would need to be perhaps 24.

Did SpaceX throttle down the booster engines on the IFT-2 test launch to prevent engine failures?
http://exoscientist.blogspot.com/2023/1 … oster.html

  Robert Clark