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Saturn V And Shuttle Questions  
User currently offlineThrust From United States of America, joined Sep 2003, 2690 posts, RR: 10
Posted (3 years 1 month 3 days 7 hours ago) and read 4604 times:

Hi there. There are several things I've been wondering, specifically with regards to propellant types, and I may not be correct about many of these. Which is actually more expensive to use in terms of per unit or however you can equivocally compare them in terms of cost, RP-1 and liquid oxygen or aluminum perchlorate, as used by the shuttle? I'm not knowledgable about rocket fuel, so bear that in mind.

Second, I'm wondering what's better....less mass in terms of dry weight, and more in terms of propellant, or less propellant and more mass? The reason I ask this was that for as heavy as the Saturn V was, in terms of dry weight, even as a whole stack with the Apollo spacecraft, it weighed considerably less than the shuttle. It also was able to launch more "clean" payload...100,000 plus pounds to the moon compared to the shuttle's 50,000 pounds...Skylab was much heavier than anything the shuttle system could've launched.

The one thing I am wondering about is whether it is a good or bad thing that each F-1 engine consumed roughly 3 tons of fuel per second, vs. the roughly combined 24,000 pounds of fuel per second that the solid rocket boosters consumed.

I'm also curious as to why they chose to have the shuttle's "stages" burn at the same time, instead of separately like the Saturn V. I'm not sure what the advantage or disadvantages of that are, if there are any.

The last thing I was wondering was about the issue of expendable vs. reusable....while it is certainly more costly to produce more spacecraft, the maintenance costs of spacecraft seem to make the option of reusability seem less desirable, especially when an expendable rocket like the Saturn V could accomplish the equivalent of over four shuttle missions....it leads to less need to launch as often, possibly offsetting the costs of building a new rocket.

The one thing I will not dispute that the shuttle system had an advantage over the Saturn V was complexity, at least in the area of the srbs....the liquid fueled rocket system, while better for performance, is much more complex to design than the SRBs.

Your thoughts on all this would be appreciated...I am merely looking to see how informed I am, and to learn more about this stuff. I am also trying to figure out why the shuttle was designed the way it was, and how much the Saturn V influenced it, whether negatively or positively.


Fly one thing; Fly it well
16 replies: All unread, jump to last
 
User currently offlinenomadd22 From United States of America, joined Feb 2008, 1896 posts, RR: 0
Reply 1, posted (3 years 1 month 3 days 7 hours ago) and read 4587 times:

You need to check your numbers. A loaded Saturn V at 3300 tons weighed a whole lot more than the shuttle stack did at 2200 tons.
And the shuttle's main payload was the shuttle. Even if you subtract the engines and supporting structure as part of the launcher and not payload, STS was pushing close to 100 tons in vehicle and payload to orbit.



Andy Goetsch
User currently offlinerfields5421 From United States of America, joined Jul 2007, 7607 posts, RR: 32
Reply 2, posted (3 years 1 month 3 days 6 hours ago) and read 4558 times:

I don't believe the Space Shuttle ever came close to the 'savings' expected as a reusable vehicle. The complexity of the post flight and prep for a new flight was always very, very expensive.

The Space Shuttle was an important part of learning the science of space.

But we also learned the cost benefit of a reusable spacecraft is not achievable with our level of technology at this time.


User currently offlineThrust From United States of America, joined Sep 2003, 2690 posts, RR: 10
Reply 3, posted (3 years 1 month 3 days 5 hours ago) and read 4532 times:

Quoting nomadd22 (Reply 1):

I was referring to dry weight when I said that. Yes, I agree..."wet" weight, the Saturn V was MUCH heavier than the shuttle...a fully loaded Saturn V weighed around 6.5 million pounds, vs. the 4.4 million pound shuttle stack. Both stacks roughly generated the same amount of thrust in the lower atmosphere. The Saturn V in terms of dry weight was actually lighter than the dry weight of the shuttle stack. Most of its mass came from propellant. It was structurally quite light. And many don't like to count the shuttle as payload since it is actually part of the launch system itself...the payload that was generally counted was the payload inside of its cargo bay, such as a satellite.

With the Apollo missions, the payload was generally considered to be the Apollo spacecraft and lunar module (both of which were not part of the Saturn V itself)...the shuttle's payload in these terms would be that which it carried inside of its cargo bay.

Either way, if you count the shuttle as payload, on the Saturn V the most equivalent comparison to that would be the LEO payload of the Apollo missions, which was heavier than the shuttle was. It was heavier by about 25 tons for the J missions.



Fly one thing; Fly it well
User currently offlineThrust From United States of America, joined Sep 2003, 2690 posts, RR: 10
Reply 4, posted (3 years 1 month 3 days 5 hours ago) and read 4521 times:

Quoting rfields5421 (Reply 2):

I agree. The biggest problem with the shuttle is that it turned out to be bigger than expected, and it also seemed like it was developed in anticipation of us essentially developing in space at a much faster rate than we actually did...it was developed in anticipation of very frequent launches...when in fact many of these launches occured months apart of each other. Five Saturn V's could have gotten the ISS built over a relatively short period, vs. the 40 plus launches it took for the shuttle to get it built. Had we somehow kept the Saturn V, my personal belief is that we would have gone to Mars decades ago. In building a vehicle far ahead of its time, we set ourselves back by almost 40 years...we really haven't come a great deal further than the mid 1970s in terms of manned spaceflight...we've gone from deep space to just staying in LEO. We also wouldn't be stuck with the task of building a launch vehicle from scratch, at least to the degree we have to now, everytime we wanted to do something different in space. Von Braun had many Saturn V derivatives that could have been developed likely in a relatively short period of time had he gotten the go ahead.



Fly one thing; Fly it well
User currently offlinerwessel From United States of America, joined Jan 2007, 2392 posts, RR: 2
Reply 5, posted (3 years 1 month 3 days 4 hours ago) and read 4502 times:
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Quoting Thrust (Thread starter):
There are several things I've been wondering, specifically with regards to propellant types, and I may not be correct about many of these. Which is actually more expensive to use in terms of per unit or however you can equivocally compare them in terms of cost, RP-1 and liquid oxygen or aluminum perchlorate, as used by the shuttle? I'm not knowledgable about rocket fuel, so bear that in mind.

In terms of raw cost, RP-1 will be cheapest per pound (by a large margin), LH2 will probably be most expensive. Installed, the solids will almost certainly be cheapest - large liquid fueled engines and stages are very expensive. LH2 is a major PITA to work with.

Quoting Thrust (Thread starter):
Second, I'm wondering what's better....less mass in terms of dry weight, and more in terms of propellant, or less propellant and more mass? The reason I ask this was that for as heavy as the Saturn V was, in terms of dry weight, even as a whole stack with the Apollo spacecraft, it weighed considerably less than the shuttle. It also was able to launch more "clean" payload...100,000 plus pounds to the moon compared to the shuttle's 50,000 pounds...Skylab was much heavier than anything the shuttle system could've launched.

All other things being equal, a high mass fraction of fuel is always better (see the thread on that we have a couple of weeks ago). That being said, the drivers for the compromises change based on the use of a given stage - boosters cause much less of a penalty for extra weight than do upper stages (which is why boosters often have much lower ISPs than upper stages). For example, as Saturn/Apollo was having trouble meeting its weight limits and they were looking for places to shave weight, it was determined that you could pull one pound off the Apollo, or 14 pounds (from memory, I don't have my reference) off the S-IC, for an equivalent increase in performance. The nature of the propellants, and the associated structural issues, also plays a big role.

As mentioned many times, the orbiter itself was 3/4s of the payload. Various cargo versions of the stack (Shuttle-C, for example) were discussed that would have significantly reduced that.

Quoting Thrust (Thread starter):
The one thing I am wondering about is whether it is a good or bad thing that each F-1 engine consumed roughly 3 tons of fuel per second, vs. the roughly combined 24,000 pounds of fuel per second that the solid rocket boosters consumed.

Given that the ISPs are similar, and the total thrust is vaguely similar, a similar burn rate is a mathematical requirement.

Quoting Thrust (Thread starter):
I'm also curious as to why they chose to have the shuttle's "stages" burn at the same time, instead of separately like the Saturn V. I'm not sure what the advantage or disadvantages of that are, if there are any.

Just the way it was designed. If you tried to launch the shuttle with the SRBs and the SSMEs burning sequentially, you'd not get to orbit. They could have fixed that by using big enough SRBs (than you'd end up with a Titan III-like configuration - and they could have used a smaller ET), or using a different way to augment the thrust at low altitude (strap-on solids for the SRBs?!). At launch, it's probably best to consider the SSMEs to be the "strap-ons" for the "main" solid boosters.

You need to generate enough thrust to maintain you acceleration requirements all the way out of the gravity well. Unlike in freefall, you cannot swap burn rate for burn time freely during launch. That's why strap-ons of various sorts are so very popular. Consider that just after liftoff, the Shuttle needs about 4.5 million pounds of thrust just to hover over the pad (as it needs to fight gravity). Only the thrust in excess of that actually contributes to (velocity) acceleration. The reason the Shuttle fairly leaps off the pad compared to the Saturn V, is that the ratio of excess thrust to vehicle mass is much higher on the Shuttle. A bit of extra thrust there can greatly improve you acceleration during the stage of flight the inherently consume the most fuel, which is why seeming very small strap-ons are useful.

Quoting Thrust (Thread starter):
The last thing I was wondering was about the issue of expendable vs. reusable....while it is certainly more costly to produce more spacecraft, the maintenance costs of spacecraft seem to make the option of reusability seem less desirable, especially when an expendable rocket like the Saturn V could accomplish the equivalent of over four shuttle missions....it leads to less need to launch as often, possibly offsetting the costs of building a new rocket.

The theory is fine. A reusable spacecraft doesn't (obviously) have to be built again. Nominal fuels and consumables costs are really a small fraction of the total cost. Just think how expensive air travel would be if you had the throw away your 747 after every flight. In the case of the Shuttle, it was killed by the very high cost of recycling the vehicle after each flight, compounded by the fact that reusability required quadrupling the most expensive part of the flight - the launch - since 3/4 of the payload was now the orbiter itself. Again, what would air travel cost if your 747 needed to carry an inert 737 on its back for every flight, and needed two or three D checks after every flight? Also the low launch rate contributed to substantial overhead.

The theory is fine. The practice was that the other costs were extremely high. Which doesn’t preclude a successful reusable spacecraft in the future. Heck, had NASAs (fantasy) two week recycle time happened, the Shuttle would have been the greatest thing since sliced bread.

Quoting Thrust (Thread starter):
The one thing I will not dispute that the shuttle system had an advantage over the Saturn V was complexity, at least in the area of the srbs....the liquid fueled rocket system, while better for performance, is much more complex to design than the SRBs.

And the SSMEs made the combined development of the F-1s and J-2s look like a picnic.


User currently offlinerwessel From United States of America, joined Jan 2007, 2392 posts, RR: 2
Reply 6, posted (3 years 1 month 3 days 3 hours ago) and read 4486 times:
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Quoting Thrust (Reply 4):
The biggest problem with the shuttle is that it turned out to be bigger than expected, and it also seemed like it was developed in anticipation of us essentially developing in space at a much faster rate than we actually did...it was developed in anticipation of very frequent launches...when in fact many of these launches occured months apart of each other. Five Saturn V's could have gotten the ISS built over a relatively short period, vs. the 40 plus launches it took for the shuttle to get it built. Had we somehow kept the Saturn V, my personal belief is that we would have gone to Mars decades ago. In building a vehicle far ahead of its time, we set ourselves back by almost 40 years...we really haven't come a great deal further than the mid 1970s in terms of manned spaceflight...we've gone from deep space to just staying in LEO. We also wouldn't be stuck with the task of building a launch vehicle from scratch, at least to the degree we have to now, everytime we wanted to do something different in space. Von Braun had many Saturn V derivatives that could have been developed likely in a relatively short period of time had he gotten the go ahead.

Don't confuse the justification of the Shuttle program with the way it actually turned out.

In terms of dollars per pound, the Shuttle was supposed to be a vastly less expensive ride to orbit than the S-V (remember that the S-V was considered to be breathtakingly expensive*). It was supposed to be far more flexible, and able to launch on far shorter notice. The Shuttle *was* supposed to be the vehicle that would eliminate the need to build a new vehicle "everytime we wanted to do something different in space."

It doesn't really matter if you need more flights, if the cost per pound to orbit is lower, it'll be a cheaper way to build your space station (approximately - there is overhead to building out of smaller pieces).

It's just that the Shuttle didn't turn out as planned.


*And then we got a look at the actual Shuttle.


User currently offlinerfields5421 From United States of America, joined Jul 2007, 7607 posts, RR: 32
Reply 7, posted (3 years 1 month 3 days 2 hours ago) and read 4452 times:

One thing I always remember, and is really driven home when I walk around the Saturn V in Houston, is what Eric Sevareid said an hour or so before Apollo 11 launched. It was something close to this:

"You have to remember that despite all this amazing engineering, they are essentially sitting atop the largest conventional bomb ever built - waiting for someone to light the fuse."


User currently offlineZANL188 From United States of America, joined Oct 2006, 3566 posts, RR: 0
Reply 8, posted (3 years 1 month 3 days ago) and read 4424 times:
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Quoting Thrust (Reply 3):
The Saturn V in terms of dry weight was actually lighter than the dry weight of the shuttle stack. Most of its mass came from propellant. It was structurally quite light.

Are you taking into account the fact that the SRBs are stacked and rolled to the pad already loaded with fuel?



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User currently offlineconnies4ever From Canada, joined Feb 2006, 4066 posts, RR: 13
Reply 9, posted (3 years 1 month 2 days 23 hours ago) and read 4399 times:

Quoting rfields5421 (Reply 2):
I don't believe the Space Shuttle ever came close to the 'savings' expected as a reusable vehicle. The complexity of the post flight and prep for a new flight was always very, very expensive.
Quoting rfields5421 (Reply 2):
I don't believe the Space Shuttle ever came close to the 'savings' expected as a reusable vehicle. The complexity of the post flight and prep for a new flight was always very, very expensive.

In that regard, the tiles were a major PITA. I have often wondered if using beryllium shingle would have been a more robust solution.

Quoting Thrust (Reply 4):
Had we somehow kept the Saturn V, my personal belief is that we would have gone to Mars decades ago.

Nope. You've still got closed-cycle environmental technology issues (still not resolved), long-term radiation exposure issues, particularly during an X-type solar flare (is there a safe haven in the s/c, for example), crew psychology issues (crew size, do they form 'them vs us' sides, male-female issues) -- it's going to be 2.5 years at least with Saturn V-like technology unless you go to some type of nuclear propulsion system, and finally, the basic weirdness of Mars as we know it now versus Mars as we thought it to be 30-40 years ago (electrified dust devils, for example).

We might be getting there now, mind you.

But I still live in hope.



Nostalgia isn't what it used to be.
User currently offlinerwessel From United States of America, joined Jan 2007, 2392 posts, RR: 2
Reply 10, posted (3 years 1 month 2 days 18 hours ago) and read 4351 times:
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Quoting ZANL188 (Reply 8):
Are you taking into account the fact that the SRBs are stacked and rolled to the pad already loaded with fuel?

The SRBs are pretty heavy empty, as these things go. About 200,000lbs each. The empty S-IC was 288,000lbs (so it's thrust-to-weight ratio was about 90% higher).


User currently offlineThrust From United States of America, joined Sep 2003, 2690 posts, RR: 10
Reply 11, posted (3 years 4 weeks 1 day 23 hours ago) and read 4075 times:

Quoting rwessel (Reply 6):

That's kind of what I was trying to get at...the shuttle in theory was an excellent idea...but it failed to live up to its expectations. Instead of getting a smaller vehicle that cost much less to launch, we got a much bigger than planned vehicle that ended up being extremely expensive. Reusability is certainly the way to go, but until then, it seems like expendable rockets are not something we can just get rid of yet. I certainly agree that an enormous rocket like the Saturn V not being reusable was very inefficient...I couldn't even begin to imagine the costs of reusability for it if we were to implement them. It will be interesting to see what NASA's new proposed SLS is like...it seems to be incorporating dual technologies of both the Saturn V and the shuttle.



Fly one thing; Fly it well
User currently offlineThrust From United States of America, joined Sep 2003, 2690 posts, RR: 10
Reply 12, posted (3 years 4 weeks 1 day 23 hours ago) and read 4074 times:

Quoting connies4ever (Reply 9):

Part of what my theory came from was from Von Braun. He seemed very optimistic that Mars was within reach after we landed on the moon.



Fly one thing; Fly it well
User currently offlineThrust From United States of America, joined Sep 2003, 2690 posts, RR: 10
Reply 13, posted (3 years 4 weeks 1 day 23 hours ago) and read 4073 times:

Quoting rwessel (Reply 6):

Again, had the cost of doing 40 plus shuttle flights turned out to be overall cheaper than 5 Saturn V launches, I agree...frequency in that case doesn't matter.



Fly one thing; Fly it well
User currently offlineThrust From United States of America, joined Sep 2003, 2690 posts, RR: 10
Reply 14, posted (3 years 4 weeks 1 day 1 hour ago) and read 3888 times:

Quoting rfields5421 (Reply 2):

Agreed that the shuttle was too far ahead of its time to be cheap and practical. But the ideals of reusability, at least in the minds of those who designed the shuttle, are consistent with cheaper costs.



Fly one thing; Fly it well
User currently offlineseachaz From United States of America, joined Apr 2005, 221 posts, RR: 8
Reply 15, posted (3 years 4 weeks 21 hours ago) and read 3857 times:

Wasn't the shuttle originally designed to be a fair amount smaller then what it ended up being? Thought I read that to get the Air Force on board with the program (which was a way around a funding shortfall) the cargo bay had to be expanded to its current size in order to launch the big spy satellites. How much smaller/lighter would it have been in the original config?

BTW great thread


User currently offlinerwessel From United States of America, joined Jan 2007, 2392 posts, RR: 2
Reply 16, posted (3 years 4 weeks 18 hours ago) and read 3830 times:
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Quoting seachaz (Reply 15):
Wasn't the shuttle originally designed to be a fair amount smaller then what it ended up being? Thought I read that to get the Air Force on board with the program (which was a way around a funding shortfall) the cargo bay had to be expanded to its current size in order to launch the big spy satellites. How much smaller/lighter would it have been in the original config?

It’s hard to give an exact number, since there was no single definitive design before the USAF requirements were brought on board. One of the earliest concepts, dating back to the mid-sixties, would have had a four man crew and 20,000lbs lift to LEO. Mind you that this was long before the boost configuration was even remotely settled, everything from a winged booster to an S-IC were considered along the way, and there was lots of growth. In retrospect, starting with a small X-20/Dynasoar class vehicle, just as an R&D vehicle, would have been a much better idea.

The Shuttle ended up with about at 53,000lbs lift to LEO. A reasonable ballpark is that the USAF requirements were about a third of that (IOW, NASA was in the 35klb range before, USAF requirements added about 50%). Much of the actual mission requirements were concentrated in high inclination flights, but that’s mostly a matter of how you report the number (IOW, the USAF was less interested in flying 50,000lbs to LEO, than they were 25,000lbs to a polar orbit). So significant, but not game changing.

A bigger impact was on the size of the wings. USAF requirement appear to have significantly increased the bring-back mass, and the USAF definitely wanted a lot more cross range capability than NASA was planning*, both of which required significantly more lift. Of course NASA was looking at landing speeds nearer 250kts, than 190, which does raise some issues, too.

The dimensions of the cargo bay also increased significantly, probably netting something on the order of a 100-150% increase in volume (a certain USAF requirement was to launch spy satellites – those simply require large mirrors, and large, but empty tubes – basically Hubble-style vehicles**), but not a lot of mass increase.

So, for a rough estimate, the overall mass of the orbiter approximately doubled.

And I like to point out that the USAF, while interested in the Shuttle’s planned capabilities (the Shuttle did draw on a number of USAF studies of reusable vehicles during the sixties too), was not actively pushing for those increases. They were told to wind down the expendable programs, as all future launches *would* be on the Shuttle, and then their requirements had to be met. Of course the USAF never really go to use the polar or cross range capabilities of the Shuttle, despite blowing $4B building SLC-6 (to add insult to injury, Challenger was lost only about nine months before the first scheduled flight from Vandenberg (Discovery would have made the first manned flight*** to polar orbit).


*the USAF had a set of once-around and back to the launch site missions they wanted to fly, since the launch site moves 1500+ miles, you better be able to fly that much off to the side, especially during a polar flight.

**The USAF and friends would probably correct me and call Hubble a KH-11 size/style vehicle.

***we’re still waiting for that milestone.


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