Launch assist = more payload...?

[Boerseun]

Here's one for Pyro:

 

When launching a rocket to orbit, a vertical launch is the cheapest in terms of fuel expenditure to punch a hole through the atmosphere up into space. Any launch attitude other than vertical will require more fuel to get through a thicker slice of air. I guess this is right so far...

 

...now for my awesome idea:

 

How 'bout some form of launch assistance? Imagine - the Space Shuttle uses tons and tons of fuel even before it starts to move. Now - if, let's say, some ginormous hydraulic lift could be built into the launch pad, where the top of the lift forms the actual launch pad, and you can accelerate the entire shuttle/tank/rocket configuration to just below 10m/s before lighting the candle, you should up your payload by quite a few tons, not so?

 

I think the 10m/s limit for the lift is pretty important, so that if there's any kind of failure the launch could still be aborted without the shuttle or rocket jumping off the lift and crash or topple over due to gravity sticking it to the lift, even if the lift stops completely.

 

I don't think it'll be such a huge technological exercise, even. All you need is a few huge pistons and a sufficiently elevated water reservoir close by. All you do is check your systems, see that everything's fine and dandy, and open the water valves. The shuttle assembly starts lifting, and in the process the rockets are lit, and when they're almost at the top of the lift's reach, the rocket motors' taps are opened wide. If there's a rocket failure, the shuttle assembly won't continue upwards because it's still travelling at less than 10m/s.

 

But being the rocket scientists you are, how difficult can this be, and how much payload would you gain when you only have to light up when travelling vertically at 10m/s already? Would it be the same weight as the weight of the fuel needed to reach 10m/s in the first place? If not, I guess it should be close - and that already translates to quite a few tons.

 

Of course there are issues regarding the complexity of it all, but you can build away to your heart's content as far as the lift system is concerned - all of it stays on the ground. More complexity breeds more failure points, however...

 

Thoughts?

[Pyrotex]

Thought #1: Total velocity required to get into orbit is about 7,000 m/s. So, your piston platform, moving at 10 m/s, supplies 1/7 of 1%. Wow. One seventh of an entire percent. Well... not exactly strap-on nuclear-excited ferron boosters, but it certainly doesn't hurt.

 

Thought #2: If the rocket launches 20 sec after platform, and it starts at 0 m/s and gets to 10 m/s, then at launch the rocket is 100m above the ground. Total altitude required to get into orbit is about 300 km. So, your piston platform supplies 1/30 of 1%. Well, it's in the right direction.

 

Thought #3: We could take your idea a little further. Say we want to launch from Eastern Mexico. There is a mountain there, rather close to the Gulf, that is about 3,000 meters above sea level. The terrain to the west of there slopes gently off. Build a roller coaster. Start at sea level on the coast and haul the rocket (on its side) west at low speed, slowly arc around to the north, then the east and begin accellerating straight for the mountain. As you approach the peak, light the rocket.

 

If the rockets are "go", then release the rocket from the roller coaster at about a 45 degree angle. You should be at 3,000 meters; and 300 MPH (15 m/s). That's only 50% more speed than you offered, but it's 30x more altitude, or fully 1% of what we need. Well... STILL not exactly strap-on nuclear-excited ferron boosters...

 

And if the rockets don't light, the rocket is not released and the roller coaster arcs up over the mountain, down the other side and is braked to a stop at the coast. Fun ride.

[Janus]

Another point: By just increasing your exhaust velocity by 10 m/s (about an 0.2% increase), you actually do a little bit better on the payload to fuel ratio than you do by shaving that 10 m/s off the delta v you need.

[Boerseun]

All true. It just seems like an enormous waste to have the thing burn tons of fuel and not even move yet.

 

As to your idea, Pyro, shaving off 1% is much more impressive than my puny little plan. For some reason I can get the image of Wile E. Coyote with an ACME rocket strapped on his back on a pair of roller skates out of my mind. But don't make it sound so futile, man! Would a 1% altitude savings translate to anything usable, payload-wise? Or does the horizontal acceleration to reach orbital velocity eat waaaay more fuel than the vertical to gain altitude so that a 1% reduction in the one doesn't really mean much?

 

I know. My questions are naive and not well thought out in the least. But do keep in mind that I haven't slept more than three hours a night for almost five months now... :confused:

[CraigD]

How 'bout some form of launch assistance? Imagine - the Space Shuttle uses tons and tons of fuel even before it starts to move. Now - if, let's say, some ginormous hydraulic lift could be built into the launch pad, where the top of the lift forms the actual launch pad, and you can accelerate the entire shuttle/tank/rocket configuration to just below 10m/s before lighting the candle, you should up your payload by quite a few tons, not so?

This idea was pretty popular with NASA in the 1990s, though the systems they had in mind were much – about 30 times, in terms of speed – grander than mere hydraulic launchpad lifts to give the vehicle a 10 m/s boost.

 

To the best of my knowledge, the major project for this was know as “Maglifter”, and involved a magnetically levitated sled cradling the spacecraft, accelerating it to about Mach 1 (340 m/s) over a track about 10 km long up the side of a high, steep mountain. The general idea was to eliminate thus eliminate the first stage of a 3 stage rocket, increasing the payload-to-total mass ratio by about a factor of 3.

 

Here are a couple of old articles on the subject: http://www.aip.org/tip/INPHFA/vol-4/iss-4/p12.pdf; Maglev 2000.

 

Given NASA’s emphasis on downsizing and shifting commercial launches to the private sector, I don’t see much chance of these literally mountain-size projects being realized anytime soon. They were grand, though.

[Pyrotex]

It's amazing, though, to look at how far we have come.

 

Von Braun's first concept for a "reusable" booster system found its way into Walt Disney's Sunday afternoon television show, back in the late 50's, early 60's. For many of us, it was THE icon of what a rocket should look like.

 

Third stage was twice the size of our Space Shuttle, with a pointy nose, huge "B-52" style wings, and half its interior was fuel tanks. Second stage was much longer and flared out 3 times wider. The first stage was monstrous, almost "obese" in its girth, with four huge fins.

 

Total height of this behemouth on the launch pad was about 800 feet. ;)

 

The Saturn-Apollo rocket was only about 350 feet tall. Why the difference? Von Braun's first orbital booster system relied entirely on room temperature rocket fuels. Hydrazine and nitrogen tetroxide.

 

The Space Shuttle can carry the same payload envisioned by von Braun in his first design, and it's only 200 feet high on the launch pad, and weighs certainly less than 10% as much.

[Universal Student]

A practical system would be an electric mag-lev rail launch assist. The limiting factor is Max Q for the vehicle at the altitude of the end of the rail. Therefore, the highest mountain available would make the most advantageous launch site.