Re: Fifteen years earlier

"The Grasshopper is not capable of getting to orbit either. "

True. It's a control systems and concept of operations demonstrator.

"The DC-X flew higher, for longer and further crossrange than the Grasshopper has."

So far.

" I suspect the goal of a orbit-capable rocket's first stage landing as the DC-X and Grasshopper do is physically impossible due to mass fraction constraints,"

Then by extension you would have considered the ultimate goal of the DC-X programme (sometimes called the DC-1), a single stage to orbit vehicle with no major maintenance between flights, to have been absurd

"The RS-68 Block 1 motors used at the start of the Shuttle program were supposed to be rated for ten flights before rebuilds were necessary; in the real world they were rebuilt after every flight. "

The RS-68 did not exist during most of the Shuttle programme.

It's the expendable engine on the Delta IV and as such has 1 use, although like all liquid rocket engines it's capable of multiple test firings.

The manufacturer ID # for the Space Shuttle Main Engine (which I think is what you're talking about) is RS-25.

You might like to review the rocket equation, the thrust to weight ratio of the Merlin 1d and approximate current payload fraction of the F9. It's all down to how much of the orbital velocity each stage has to supply.

Re: Fifteen years earlier

The shuttle wasn't designed to need that much refurbishment between flights, it just happened somewhere betweeen design and reality. I wish Elon all the luck in the world.

Re: Fifteen years earlier

"The shuttle wasn't designed to need that much refurbishment between flights, it just happened somewhere betweeen design and reality. I wish Elon all the luck in the world."

No it happened when Nixon's OMB required it be built to a fixed constant yearly amount despite high inflation in the US during the development and the fact that no major aerospace project had that funding profile.

The architecture was the only one that could come close to meeting that budget profile. That design, and that apparent lack of someone in overall charge of the project, who understood the issues between sub systems and could trade their performance accordingly, are the reasons STS was what it was.

Re: Fifteen years earlier

"Being pedantic to be polite... The Shuttle's ET could have been carried to orbit; it was nearly empty at Main Engine Cut Off (MECO) and there were BOTE plans at one time to collect them in orbit to build a space station and/or orbital tank farm for fuel and consumables for Moon and Mars missions etc."

I was aware of that. I think the design went a bit beyond the BOTE stage but parts of NASA seemed to feel it was "Skylab" all over again and wanted the new shiny made-to-order space station (they would not even allow flight experiments to be attached to one of the access doors). 2 (or was it 3?) design iterations later they got it.

And not to be pedantic but the first S in SSTO stands for "Single." Actually the STS payload could have been substantially higher if NASA had recognized that lower tank pressures directly lead to lower tank mass (and within 150m/s of orbital velocity tank mass translates more or less directly into additional payload). SSME tests indicated it could comfortably support lower tank pressures.

"The Shuttle was unique in that its main engines burned from takeoff to orbit, a critical part of an SSTO design I think you would agree."

IMO the SSME was one of the "crown jewels" of STS development. Had all upgrades been implemented it would have been even better(at least 300lbs lighter, more if you can dump the 6 stage LP LOX drive turbine, less inspection etc). The issue was (given its size) how to make effective use of its capabilities.

"The Soyuz capsules already use rocket braking to soften their landing but it's not a zero-zero landing system, it just takes some of the energy out of the ground impact after the parachutes have bled off most of the vertical speed."

Irrelevant in this context. This is a stage, not a capsule. The aspect ratio of diameter to height is part of what makes it tough.

"As for the Dragon capsule being "cramped", I'd compare it to the Shuttle's accommodations which were spacious in comparison for the same planned crew capacity, seven. It's also missing a toilet, one of those luxuries that you get to appreciate after your tenth day in orbit from what I've been told. No shower either."

The Shuttle was designed to be the sole on orbit accommodation for the 7 person crew for up to 14 days. Crewed Dragon, CST-100 and Dream Chaser are designed to be buses to the ISS, not camper vans.

Re: Fifteen years earlier

"Yep, RS-25 not RS-68 as you said."

RS-232 has nearly sent me into orbit a couple of times...

Re: Fifteen years earlier

"RS-232 has nearly sent me into orbit a couple of times..."

So true. So true.....

Joking aside the 422 version is quite popular for some launch vehicles. The differential signal format makes it much more resilient to electrical noise (lots of high current pulses flying around).

Re: Great job of controlling that rocket....

" and then the detached boosters turn around and fly back home and land vertically."

The trick (or part of it) is to avoid having to "fly" them back. It's more like a sort of controlled "fall" back from orbit.

"I'd think the amount of extra fuel, structural weight and complex control and telemetry systems to make this work would more than outweigh the cost of using a good old-fashioned "let's fire it and drop it in the drink" reusable booster like the space shuttle had."

That's what Spacex is trying to find out. But those SRB's took serious refurbishment (At one time the new cost was equal to the refurb cost, which sounds highly suspicious to me). And of course transporting roughly 1million lbs of explosive from Utah to Florida per booster. Do you think having a solid rocket booster mfg plant in a landlocked state and making them so big they cannot fit in one piece onto a train was a bit of a design oversight?

Re: Great job of controlling that rocket....

@ Robert Sneddon

Exactly the point I was trying to make regarding the use of ocean as downrange for launches. After you've left Cape Canaveral or Vandenberg, the next piece of terra firma to land on is going to be Bermuda or Hawaii. So to make this work you'd have to boost your payload up to several thousand miles an hour, separate and then turn the boosters around and fly back to Vandenberg or Cape Kennedy. Both of those coastlines (Southern CA and central Florida) are heavily populated, so there are no real alternatives to land anywhere else.

Seems to me that structurally that 180 degree turn at such speed would be very stressful on the booster, which would still be in the atmosphere, and would take a great deal of fuel to perform that maneuver. So not only would you have a structurally larger booster, to carry all that extra fuel and control systems, but it would have to be a structurally more rugged booster too, to handle the stresses of performing the turnaround maneuver in the atmosphere.

At that point, I would think it would become impractical. Maybe you can actually orbit the boosters and have them land back home (or at Edwards AFB or Kwajelain some place like that) after completing pretty much a full orbit, but then you have to worry about re-entry, while carrying lots of explosive fuel to make the vertical landing .

Re: Great job of controlling that rocket....

"So to make this work you'd have to boost your payload up to several thousand miles an hour, separate and then turn the boosters around and fly back to Vandenberg or Cape Kennedy."

No. Following separation the stage continues to coast to high altitude. At that point the wind resistance is practically zero (close to space vacuum) and the force needed to spin it round is pretty low. Those 9 engine bells make pretty good air brakes. Those two details make a bigdifference to feasibility. How big is the key question.

"At that point, I would think it would become impractical. "

Well that's part of the point of these tests. You might like to revise you views given that how you think this is going to fly is incorrect.

Re: Whoa! Very sweet trick

"Kind of strange watching that footage, when I consider that the last time I saw a rocket rise off the pad and hover like that was the attempted launch of Vanguard I"

Well there was also that Lunar Lander Simulator that Buzz Aldrin was flying (the flying bedstead IIRC was one of it's nicknames).

Jet engine to cancel 5/6 of the mass so the lander rocket engine though it was in 1/6 g.

Good thing they went ahead and fitted the ejector seat anyway though.

Re: Whoa! Very sweet trick

"Seriously, man... the LLRV was a wicked-assed machine -- literally. From all accounts, astronauts training to fly the LM swore by the LLRV, and at it. Neil Armstrong was nearly killed in the LLRV training for his Apollo mission."

I think it was Buzz Aldrin but it was their instantaneous recognition that a)something was wrong b)they could not fix it and c)time to eject that demonstrated they were the 1st choice for the first Apollo landing.

Proving that one man's wicked ripping fun is another man's insanely dangerous kamakaze death ride.

Having read descriptions of it I still can't tell if the on board computer helped you compensate for the weight changes as the fuel ran out. The lack of this is one of the things which makes the various rocket belts built over the years (I did not know that Bell built both the rocket belts and this simulator) so tricky to fly (and why there are few people licensed to fly a rocket belt than pilot an LM).

Re: Bah they are as bad as those Wright brothers

"ITS A FSCKING PROTOTYPE NOT AN END DESIGN"

It's not even that. It's more like a proper X vehicle. It's mission is to gather information so the real vehicles can be be built. The X1, X2 and X15 (and most in between) never turned up as actual production aircraft but what was learned drove most supersonic US aircraft and missile design for decades(including the space Shuttle)..

Thumbs up for making the point.

"Obsolete junk. What really needs to be done is throw lots of money at the Skylon people. Real, surface to space jet/rocket hybrid engines which look EXACTLY like the engines from just about every one of the more awesome sci-fi spaceships? (The atmospheric capable ones at least!) I'll buy that for a dollar!"

Sold! To the man with £12Bn in his bank account.

What's that. You don't have £12Bn in your account?

Skylon's capabilities are indeed very impressive. They are also still highly speculative (but becoming less so each year). And that is there estimated total budget.

Re: Navigation Budget

"I don't think the first stage has anything like the energy at separation to make it across the Atlantic on its own."

You're probably right. If it coasts to maximum altitude it's forward speed is zero. At this point it could fall vertically or be given a reverse thrust which starts it on a parabolic fall back to the area of the launch site.

"The Spanish landing strips for the Shuttle abort plans required the Shuttle to continue in powered flight for several minutes with or without the SRBs. "

With the SRB's providing c90% of the thrust (and being impossible to shut down without the loads tearing the stack to pieces) I'd suggest that would be with the SRB's attached. I think you'll find the technical term for the crew of a Shuttle that has one or both it's SRB's detach while still firing was "dead."

"The first stage of a three-stage stack like the venerable Saturn V separated about 50km up at about 3km/s velocity,"

The Saturn V stack used 2 stages to achieve orbit. The third was the Earth departure stage for the Moon. Given most flights were to the Moon (or around it) that's the configuration that tended to fly. The usual rule of thumb is the delta-V for orbit with 2 liquid stages is about 50/50 between the 2 stages. Black Arrow was unusual. It's first stage supplied about 1500m/s. A big chunk was supplied by the 3rd stage Waxwing solid. This fact is under appreciated by people who have seen it in a museum. Orbital velocity is about 7950m/s but losses typically bump it up to about 9100-9200m/s. Shaving those losses pays very big dividends.

This stuff might look to you like the "same old same old" but it's not. Building a new gas generator LOX/RP1 rocket engine (albeit one with a pretty good T/W) is rocket engineering. Likewise building a good lightweight tank structure is also engineering. There is lots of prior art on these areas.

Actually learning how to land a stage of a TSTO vehicle is rocket science. Yes that aspect ratio makes a hell of a difference which DC-X (along with other SSTO concepts, especially those of Philip Bono) designed out. But you cannot build a TSTO that shape. Musk is trying to square the circle, which is why this is "super damm tough." As old maps put it "Here be monsters," and yes he may fail. But his team have gone further than any previous AFAIK with dealing with real world size (and shaped) hardware.

You might find the work of John Carnack and his team at Armadillo aerospace instructive. From PC game programing to hardware hacking on large scale. Reading through their back posts is highly instructive, especially how supposedly trivial issues can bite you. How what seem to be fairly easy performance specs require top class components and near semiconductor levels of cleanliness.

Keep in minds most of there stuff has been relatively well behaved liquid fuels. Not giant explosive SRB's or vicious hypergolics.

Re: Navigation Budget

"SRBs are incredibly well-behaved compared to LOX plus anything with carbon and/or hydrogen in it and a lot easier to handle and store, one reason most military missiles use solid fuels these days."

Solids make excellent weapon systems. Except the filling of the Shuttle SRB's, which slumps over time.

There virtues (storage vessel is combustion chamber, mechanical simplicity, once started never go out) are either irrelevant to commercial use or active liabilities. LOX is dangerous due to it's concentration and temperature. In time it warms up and diffuses into the air. In contrast both solids and hypergolics are intrinsically dangerous. Solids don't evaporate and a cloud of UDMH is an effective chemical weapon.

When solids are built, moved or stacked they are classed as an explosive and the expenses are those of an explosive, not a set of propellants which can be moved separately.

"The material they're made of (an auminium powder and perchlorate mix plus a binder in the case of the SRBs) doesn't explode"

Under normal circumstances, but solids have exploded and the combustion of 1.1 million lbs of explosive is pretty serious. The normal physics of operation are deflagration but it can move into the detonation regime (and has) and the transition process is not that well understood. It used to be thought hybrids were immune to this, but even they are not.

"If the flame had been directed towards the outside of the stack away from the ET then the Challenger would probably have survived and made it to orbit."

Highly doubtful. At that point you have a case weak spot and increased burning area of the grain. You now have a thrust vector acting on the stack it was never designed for. If this SRB fails you've now got massive force imbalance on the stack. If it does not you have a (growing) side force until the SRB burns out (prematurely) leaving the other (because you cannot shut them down) SRB to rip the stack apart.

As for the contention that only Thiokol could build large solids and my recollection there were at least 3 companies that could perhaps you should look at this little item on Shuttle design choices and mfg selection.

http://www.tsgc.utexas.edu/archive/general/ethics/boosters.html

"I don't know what fuel the Dragon capsule's LES is going to use. I presume it will be storable hypergolics such as UDMH and N2O4, not something I'd be comfortable sharing such a compact capsule with in quantity."

Agreed but they are the common state of practice. Again what does that have to do with Grasshopper, which is mostly LOX/RP1?

Re: Nice test

"I wonder how well this would work on Selene or Mars?"

Good question.

Obvious answer. Badly.

Mars atmospheric pressure is about 1/1000 of Earth sea level at Mars sea level.

The Moon is worse.

Air drag is an integral part of the process. While the lower gravity of Mars or the Moon helps I don't think the balance of forces works out too well in either case. I think you'll need more terminal thrust (but OTOH the propellant to do so weighs less). Lots of testing needing.

Thumbs up for the question.

Re: Pilot required?

"To me the spaceplane idea such as SpaceShipTwo, where the whole launch vehicle returns under pilot control, seems a more practical and politically-acceptable idea."

Despite its name SS2 is sub orbital.

It's maximum speed is about M3.

And no the airframe is unlikely to manage roughly 7x increase in speed (and the roughly 49x increase in kinetic energy) needed to reach orbit.

Re: Pilot required?

".....And no the airframe is unlikely to manage roughly 7x increase in speed (and the roughly 49x increase in kinetic energy) needed to reach orbit." Don't be silly, the whole idea of SS2 is the launch vehicle carries the orbiter to a high altitude, saving the orbiter from having to carry the extra fuel and engines required to reach that altitude. The orbiter, effectively a small shuttle, then separates and uses it's own rocket engine to shoot into orbit. The launch vehicle is analogous to the boosters on the Shuttle, only it takes off and lands like a plane and is re-useable.