ESA lifting body entry vehicle on the cusp of final approval

[phongn]

But making it lighter would have made either its payload bigger (bigger than 25 tons? why would you need that at all?), or decreased the size and complexity of the launch system overall (like for example using only 2 SSMEs).The second option would have dropped the launch-rate-to-go-even down to something that could have actually happened and you would have had a Space Shuttle that was actually a success and would still be operational today (maybe with new improved orbiters). Not 25 launches per year, which was insanity at the day and is still insanity today.

No, the problems with STS are the large fixed-costs involved in dealing with the TPS (and if you keep an aluminum airframe, you still need the highly conservative design). SSME itself is a problem - going from three to two doesn't really buy you much. The engines are still tremendously complicated machines. You still need cross-range to satisfy USAF requirements. Mass is the least of the concerns with STS.

[erik_t]

Having two SSMEs implies severe abort mode problems. This was studied intensely during the STS design process, obviously. TPS could be rather less conservative in a notional 'flight II' shuttle, but only by building off of knowledge from the first flights.

[Skgoa]

SSME is a great engine. If we are talking about a drastically slimmed down orbiter, Two engines running longer might actually be worthwhile. And have these abort modes ever been needed? Nothing comes to mind, but I am very drunk and its almost 2 am over here...

What made them think they could do it? How much was inexperience, how much was things like trouble with the heat shield?

What exactly do you mean by that question? The Shuttle fullfilled almost every goal set during the design/planning stage. (Including it's cost goals, btw.) Its not the system's/engineer's fault the end user of a product only uses it a few times a year, even though almost all costs are fixed regardless of actual usage. The only big thing that comes to mind is that the tiles of the TPS had to be reduced in size (and thus raised in number) due to fear over their stability. This greatly increased the necessary amount of maintenance that has to be performed between flights. The orbiters have also shown a resilience that they weren't even designed for. That we are seeing more and more problems is mainly due to a) them being around far longer than they were ever meant to fly and/or b) NASA flying them outside their design envelope. (Thats the reason for the Challenger desaster. It was never ever supposed to be launched in those weather conditions.)

[Simon_Jester]

What exactly do you mean by that question? The Shuttle fullfilled almost every goal set during the design/planning stage. (Including it's cost goals, btw.) Its not the system's/engineer's fault the end user of a product only uses it a few times a year, even though almost all costs are fixed regardless of actual usage...

What made them think they could refurbish an orbiter in a matter of days, when in practice it took months? Were the end-users at NASA just dawdling and moving slowly on refurbishing before each flight for some absurd reason? I would think not; weren't there times when people would have been happy to fly more frequent shuttle missions? Say, while assembling the ISS?

If NASA wasn't deliberately slow in turnaround for the shuttles, why did it take so much longer than expected to get them ready for the next launch?

[Skgoa]

Did it actually "take" as much time as you think? I mean turn-around could have been much faster than what it was historically. E.g. the orbiters were actually put in vertical storage for weeks or even months between missions. So observed flight dates is not a good indicator of what NASA would have been capable of. Missions are planed and hardware is contracted years in advance. Being able to fly sooner doesn't make the payload manufacturers work any faster or the bean counters (administrators, civil servants, politicians...) spend funds any more willingly.
Another thing to remember is: the big unanticipated problem of the program was the TPS*, they just didn't expect there to be so many tiles and to have to inspect every last one of them between flights. Its a pain in the ass and its part of the reason why the "standing army" that refurbished the orbiters was so large.

*i.e. the heat shield, for those who aren't as knowledgable about these things

[someone_else]

No, the problems with STS are the large fixed-costs involved in dealing with the TPS (and if you keep an aluminum airframe, you still need the highly conservative design).

The smaller the orbiter, the less surface to place TPS you have. Surface decreases more slowly than mass, but that is.

Having two SSMEs implies severe abort mode problems.

Even for a smaller orbiter? I was thinking about leaving the performance the same, but decreasing the wasted mass will mean that after you cut enough, three SSMEs become overkill.
But it was not a thought out proposal, just an half-assed example.
If it's the number what matters, then you have to make them smaller.

Its not the system's/engineer's fault the end user of a product only uses it a few times a year,

Well, if the cost to use it is higher than using another rocket... free market will decide. And it had a high $ per Kg cost if I'm not mistaken, scaring everyone away (even the USAF, although it realized it was far less flexible than firing off a couple standard rockets when needed).
After the fell of the URSS lots of far cheaper rockets with similar payload were available.
If you base your design on the assumption that everyone will have to buy your service because you say so (and only then the costs will go down), that isn't going to end well.

The same problem of the current Big Dumb Rocket developed post-Constellation. But worse since none other than the US government will pay for its services due to very high price tag.

[Skgoa]

No, the problems with STS are the large fixed-costs involved in dealing with the TPS (and if you keep an aluminum airframe, you still need the highly conservative design).

The smaller the orbiter, the less surface to place TPS you have. Surface decreases more slowly than mass, but that is.

Actually, due to the fact that you want to slow down at a specific rate, the square-cube-law might not actually have as much effect. You don't have that much leeway to move from a linear 'weigth <-> survace area' relation, if you want to do unpowered re-entry. I am not making an argument for or against either of you two here, its just meant as a heads-up.

Having two SSMEs implies severe abort mode problems.

Even for a smaller orbiter? I was thinking about leaving the performance the same, but decreasing the wasted mass will mean that after you cut enough, three SSMEs become overkill.
But it was not a thought out proposal, just an half-assed example.
If it's the number what matters, then you have to make them smaller.

The Shuttle has some reserve thrust, so for a big portion of it's way up a failing engine would not endanger the mission or at least mean an abort to an airport. Thats a much better situation than loosing the whole spacecraft. Having only two engines would mean that the shuttle could loose not only a higher fraction of it's "normal" thrust, but also a proportianlly higher part of it's "reserve", too. Now, if your smaller orbiter is significantly lighter, that might not actually be a problem. In that case you might even want to go with three SSME and no SRB, though. (One would have to do the math, but IMHO it might be possible, but would most definitely not be cost effective.)

Its not the system's/engineer's fault the end user of a product only uses it a few times a year,

Well, if the cost to use it is higher than using another rocket... free market will decide. And it had a high $ per Kg cost if I'm not mistaken, scaring everyone away (even the USAF, although it realized it was far less flexible than firing off a couple standard rockets when needed).

The military had it's own turf war going on behind closed doors. In the end it was their requirements that drove up cost and that made them abandon the Shuttle. But in the early 70ies, there was only one LV of that payload class going to get built, so they HAD to get on board.

After the fell of the URSS lots of far cheaper rockets with similar payload were available.

Yeah, but we are still talking about the Shuttle. At that time there were better rockets in the West, too. IMHO some US administration should have funded developement of a successor to the Shuttle somewhen around that point.

If you base your design on the assumption that everyone will have to buy your service because you say so (and only then the costs will go down), that isn't going to end well.

Then its a good thing NASA never made that assumption. Cost wise, the assumption was that the government would pay for a high number of launches/missions and thus the Shuttle would be cost effective... which would lead to the private sector getting on board. As it turned out, not even the administration that approved the begin of the Shuttle's developement was ready to fund anything else and the military was very slow to get on board. The design was never based on this assumption, though. It was based on requirements and on a budget - both of which mostly got handed down to the engineers from higher up.

The same problem of the current Big Dumb Rocket developed post-Constellation. But worse since none other than the US government will pay for its services due to very high price tag.

[/quote]
Why Congress has mandated a new Heavy lift LV without adequatly funding it or any missions that utilize it's capability is beyond me, too.

[Sea Skimmer]

What exactly do you mean by that question? The Shuttle fullfilled almost every goal set during the design/planning stage. (Including it's cost goals, btw.)

The ones it missed proved important though, as it never did met the specs for the military polar orbit missions which took an awful lot of military payloads out of contention, and then once the Vandenberg pad was killed as a result that this also killed off using it for a lot of civilian weather satellite and land sensing satellite missions. If polar orbits never entered the equation the shuttle could have had smaller wings and generally worked better and cheaper. I forget how much money got wasted doing work at Vandenberg but it was a lot, like two billion dollars.

[Simon_Jester]

In what regards did the shuttle prove unsatisfactory for military polar orbit missions?

[Sea Skimmer]

Not enough cross range in orbit or during recovery, the military wanted very rapid recovery to avoid ASAT attack, and less then desired payload to orbit. The government was still prepared to just accept the limitations and go ahead with civilian polar launch stuff, until the Challenger disaster meant they wouldn’t even be able to use to Vandenberg facility on schedule, while the military stuff simply had to be launched, as well as raising safety concerns about its physical layout, so it was canceled. Likely for the better in the end run since shuttle production ceased anyway.