Is there a safer way to orbit?

Factual Questions
1

Launching vertically has been the only option for most of the history of space flight, but new technologies are making possible a better way to put people into space. A two-stage to-orbit, totally reusable space plane is an important step in making space exploration a manned enterprise. Taking off straight up requires everything to work right, and gives very few opportunities to abort the lift off.

Right now, to rotate the crew on the International Space Station requires at least two launches, and that is just for six people. We need something which can carry at least a dozen passengers, safely and routinely, so that crew rotations on bigger space stations do not require lots of launches. And the concept I am advocating is only for people; cargo can, and should, launch straight up.

By using an air-breathing, horizontally launched first stage to carry the orbiter to altitude, many abort options become available. To begin with, a launch track would be required, instead of a runway, and the magnetic catapult would be able to stop the launch stack in event of a refused take-off. This catapult is only to accelerate the stack to about 500 kilometers per hour, which is how fast I figure the wing will have to go to be able to lift off. The catapult will reduce the length of the launch track considerably, as fan jets are very slow to accelerate.

Because the wing will have to lift a fully-fueled orbiter, plus its own fuel, I figure take-off weight will be around 1 million kilograms. To accomplish this, I visualize a bi-plane, with an upper wing which is inflatable, so that it can be deflated after the orbiter launches. Overcoming all that drag will require 10 or 12 of the biggest fan jets available, but at least there will not be much weight involved in an undercarriage, as the launch track will support the wing.

The orbiter will have to ride on the carrier wing’s back, as it will be too large for the wing to straddle. Also, the orbiter will light its engines while still on the carrier wing, and then fly off. This way, no altitude is lost, and high g pull outs are avoided. Because the orbiter will not be a heavy lift launch vehicle, and it will not be taking off straight up, it will not require large, powerful engines. Exotic, difficult-to-handle fuels such as liquid hydrogen won’t be needed. Everything about this spacecraft will be designed with robust safety margins.

Having the passengers suit up to transfer to the space station or ferry vehicle would be wasteful, and would require considerable extra weight. Instead, the passenger compartment can be lifted out of the payload bay with an arm, to be swapped with one containing passengers heading back to Earth. The passenger compartment would have built-in life support for the transfer, although I am not sure if it will have a zero-gravity toilet.

The orbiter would land on a runway at the launch site, using extendable wings to reduce stall speed. Sufficient cross-range capability would allow for alternate landing sites. Landing the carrier wing will be much more difficult, as the wing will be very difficult to handle in cross winds. I propose that the launch track be used as a means of allowing the wing to mate with a sled being moved by the magnets on the launch track. This would allow the wing to land at a higher speed, maintaining control even under severe crosswind conditions.

Turn around time on the carrier wing would be very short, probably under 24 hours, so only a few will be needed. Orbiters will have much longer turn around times, but a sufficient number will allow launches as often as necessary.

2

An inflatable wing? Made of what, now?
I’m not sure I understand exactly all the different steps in your proposed launch profile, but it sounds somewhat similar to what Virgin Galactic is currently working on with White Knight Two and SpaceShipTwo, but that is not capable of reaching orbit. They’re working on a compatible spacecraft, LauncherOne, that is capable of reaching low Earth orbit, but it will only be capable of carrying a payload of about 500 lbs.
I think you have a lot more to work out than just whether or not to include toilets in your passenger compartment.

3

Stratolaunch was developed to launch large rockets from an aerial platform. It didn’t have the OP’s complicated launch track and so forth, just a humongous two-fuselage plane. However, since Paul Allen died, it’s become the world’s largest white elephant.

4

First, a reminder that space isn’t far away, it’s “fast away”. Most of a rocket’s fuel isn’t used to go up, it’s used to go fast.

With that in mind, how do you plan to get the orbiter from the 500 km/h speed of the wing up to the 28,000 km/h speed required for low earth orbit without using “exotic fuels”? Even if 500 km/h is just the takeoff speed of the wing, and the cruising speed is something closer to Mach 1, you’re still looking at a required change in velocity of 26,000 or 27,000 km/h.

5

What MikeS said. Building a spaceplane that can reach an altitude of 400 kilometres (where the ISS orbits) in one or two reusable stages is probably feasible - the X-15 reached more than 100 kilometres (a widely used definition of the lower bounds of space) with 1950s technology. The problem is getting it to such an altitude and accelerating it to the ~28,000 kmph of orbital speed that it needs (going sideways, not upwards) to stay there.

6

Once you are up that high and moving at what I recall might be 20% of orbital speed, the amount of fuel needed to accelerate into orbit is manageable with existing rocket technology. You’ve already done a lot of the hard work by reaching that altitude and velocity. Of course the X-15 wasn’t launched from the ground, a two stage to orbit plane is getting pretty large when all factors are considered. One theoretical possibility is refueling in the air at high altitude to allow a space plane to take off horizontally like a conventional plane, but that just adds more complexity.

7

Kerosene and liquid oxygen have put a lot of stuff into orbit. Exotic fuels are used to get every possible bit of performance, which is what this concept is trying to avoid. (Think of school bus.) By launching the orbiter above the majority of the atmosphere, most of the fuel will be used for acceleration, not fighting gravity going straight up.

A vehicle about the size and shape of the Space Shuttle, but without the massive payload bay and the huge engines, could carry enough propellant to reach orbit, if the payload is only about 7,000 kilograms, and the launch pad is 14 kilometers up.

8

Stratolaunch requires a massive runway, and the undercarriage weighs several tons. What is a fuselage for? Carrying cargo and passengers. The cargo the carrier wing needs to carry must be able to separate from the wing without being dropped.

My idea does away with all the weight of an undercarriage, and the expense of several kilometers of concrete 3 meters thick. And, up until the moment of take-off, the launch can be aborted without damaging the vehicles. If a failure occurs after take-off, the orbiter can light its engines and fly off of the wing, to come around and land. And an abort is possible at every stage of the launch, up to and including an abort to orbit.

By using several engines, with at least on of them capable of being throttled, the thrust can be kept below two gravities. During landing, at least one of the engines would be capable of firing, so dead stick landings are avoided.

9

The enemy of reliability is complexity.

Current rockets are very reliable, and the number of crewed aborts very low compared to launches. As complexity increases, you may find all the complexity in the abort systems becoming the main reason you need to abort.

One notes that conventional rockets safely abort launches right up to the point of lift-off. Only the shuttle didn’t have a pad thorough to to orbit abort mechanism. All the current and planned ones do.

There is a lovely recent interview with Elon Musk done by Tim Dodd (the everyday astronaut) where Elon talks about simplicity in design. I think anyone involved in engineering design should watch it.

10

What do you reckon your magnetic catapult will cost?

Note that a fair few of those expensive concrete runways already exist, and are in fact rather cheap to use.

So an expensive runway is required?

11

So the idea of a plane launched rocket has been around for quite some time. Virgin has one working now for sub-orbital flights right now. Test rockets have likewise been launched this way. But they have never been heavy, and IIRC never orbital. I do suspect that is a hint of a reason. It may not scale up, and the amount of configuring you add like a inflatable extra wing speaks to that as a real issue.

What the vertical launch is doing is getting the orbiter away from the dense lower atmosphere ASAP, where it can better accelerate against air. In a rocket it had power, but fuel is limited, so straight up makes sense, however in a plane, especially a very heavy plane, you will have limited power, but much more fuel, so a horizontal flight pattern using lift to gain altitude and taking quite a bit more time makes sense. However is a plane, and a very exotic plane for that matter, make sense over a slightly more powerful rocket and some extra fuel?

You also have the extra complication of the safe separation of the aircraft to the orbiter, which is moving the liftoff from ground to air, but still has much of the same complications - remember when the orbiter separates it’s going to want to come down, while the plane unloading the weight will want to go up under lift . I don’t think it’s as easy as you state, and the craft still have have to go through the stressful acceleration engine light off stage, we can read about that in Virgin’s accounts when the rocket motor engages.

12

The Pegasus rocket, which launches from an aircraft, has put payloads in orbit. Small ones though, so doubts about scaling it up are valid. Stratolaunch was planning on launching Pegasus, except as many as three at a time, as I understand it. Well, not three at exactly the same time, but three on a single Stratolaunch flight. However, something fell through on this (and I can’t remember what), so Stratolaunch started to develop their own rocket to be launched. That was cancelled when Allen died.

The OP’s plan for landing the carrier plane is questionable. Since the carrier doesn’t have an undercarriage, the idea is to land it on the track it was launched from, mating it with the sled at a fairly high landing speed. Has this kind of landing ever been done before?

13

Again, this is not an issue. Rockets don’t go “straight up” and objects in orbit still experience a large majority of surface gravity. Most of the rocket’s fuel is already used to accelerate; the lost acceleration due to gravity is minuscule. It’s not effective to develop a highly complex alternate system to further reduce it.

14

Except the Pegasus which launches horizontally from an airplane.

Why this configuration in particular?

Not really. All human-rated rockets have redundancy and abort modes. Though of course some are worse than others (e.g. the Shuttle had very limited abort capability compared to newer rockets currently in development).

And why is it a problem that it takes two launches to send a full crew? Seems like a good practice to replace only half the crew at a time, to provide continuity.

Are you conceding from the start that it’s more expensive than launching straight up?

Yes, the catapult could stop the spacecraft, but only if there was enough track left to slow down and stop. So really, this abort mode is only useful if something fails during the first few seconds - e.g. engine failure. Then again, on a conventional (vertical liftoff) rocket, if the engine fails immediately upon ignition, before the rocket leaves the pad, it can shut down all engines and abort. Some (e.g. Soyuz) have clamps that holds the rocket down until the engines are started up.

Also, what if the rocket catches fire and explodes right after ignition? On a conventional rocket, the escape rocket ejects the crew capsule away from the exploding rocket. This doesn’t sound like an option for your spaceplane.

How did you come up with this number?

Not sure where to start. The wings need to be strong enough to lift the weight of the entire aircraft/spacecraft, because that’s what wings are for. So you can’t have wings that are supported by the launch track. And how would inflatable wings support that much weight?

Why would a horizontal launch require less powerful engines than a vertical lift? Whatever the orientation, the purpose of the engines is to (1) overcome air resistance, and (2) accelerate to orbital speed. If anything, horizontal launch would require more power because it would take longer to get out of the atmosphere.

Which is why no spacecraft in history has used that method of transferring to a space station or another spacecraft. You just connect the docking ports and float in through it.

Why extendable??

Is there any abort mode for a failed landing (e.g. not lining up correctly with the runway)?

You say cross-wind would be a problem, yet you propose using the launching track for landing, which means you can’t choose which direction to land??

15

There may be a safer way to orbit, but this Rube Goldberg contraption isn’t it. This is more like, “Hey, what if we took rocket launch and made it much more complex, with a whole bunch of new critical failure points?” It’s hard to imagine a mode of launch more dangerous than trying to launch an airplane down a track with a fully loaded orbital rocket on its back. And if that rocket goes boom at any time, there’s no escape system for the astronauts or the flight crew. And that moment of separation would be a doozy. What is the plane below going to do? Release the clamps and then go into a high speed dive to avoid the multi-hundred thousand pound bomb falling above it? Or does it just sit there while the rocket lights its massive engines and attempts to roar away without a collision or frying the plane? And this is a safer solution than just launching a rocket from a pad?

Aerolaunch was never about safety - it was an attempt to lower the cost to orbit. But it was comparing itself to the outrageous launch coats of the traditional aerospace companies, and compared to them a case could be made that small payloads might be cheaper to launch this way.

The era of reusable rockets is going to make air launch obsolete. In fact, a mature reusable rocket industry could make the concept of a space elevator obsolete, as reusable rockets can theoretically be cheaper.

There may be one safer way to get to orbit - by balloon. The concept is that you ride one balloon to a much larger, floating platform at 140,000 ft, and from there you get into a gigantic, mile-long balloon that rises to 180,000 on lift, until the air is too thin to support the balloon. Then the balloon fires ion engines to accelerate it horizontally. As it accelerates it gets aerodynamic lift from the sparse molecules of near space, but drag is so low that it can keep on accelerating and surfing on air molecules until it is in orbit. The process would be slow and careful and very low stress.

To come down, you reverse the process, descending over days or weeks by very slowly braking with ion engines until you can start getting aerodynamic lift from the atmosphere. then you just slowly brake until you descend back to the stratosphere station, then you get back into your smaller balloon and make a peaceful, quiet slow return to Earth. No significant atmospheric heating, no heat shield required, and the whole system could be solar powered.

In theory, the math appears to work. The devil, as in all big engineering projects, lives in the details. But if we could make it work, it could be made extremely safe in time.

16

This is the key point - For a decent sized orbiter, you still have some powerful rocket engines on a massive load. We can see from vertical launches what this means - a huge flame shooting out the back of the orbiter.
This means that the launcher has to get the hell out of the way before the engine fires; meaning some serious maneuvering while the orbiter is just an unpowered projectile, losing speed or height (or both) waiting for the launcher to get out of the way.

Plus, there’s the problem of creating an aerodynamic launcher. the logical configuration is the orbiter is under the launcher, since when the load is dropped, the launcher will rise. An orbiter on top (like the Shuttle/747 transport configuration) means more complex maneuvering to separate, and the orbiter needs sufficient aerodynamic lift to rise above the launcher without power - and this is a very risky maneuver compared to dropping. If you light the engines before decently separated, you are basically blowtorching the launcher during separation- not the best technique for a thin-skinned aluminum structure carrying jet fuel… or humans.

Also, what do you gain? A flying body unless incredibly powerful will be subsonic, and probably only fly to 50,000 feet or so at most. How long after liftoff is a vertical rocket going 500mph? How long before it’s at 50,000 feet? It’s probably simpler to strap on some solid boosters than build a complicated air launch system.

You don’t want to make a launcher go much faster, since who knows what happens when you drastically change aerodynamics at, say, Mach 5? The 600mph is almost nothing compared to the 18,000mph or so needed to orbit. The only real gain is getting out of the thicker air.

There’s a reason that big aircraft (bigger than a fighter) don’t use variable geometry wings. The size of the pivot hinges, the strength of motors to extend wings against drag at almost mach1 - not going to happen for an airliner-sized craft. Inflatable, even worse. Not feasible with current technology.

The trouble with catapult tech is that it adds speed in short distance using high acceleration. Modern rockets pull a few Gee’s; but most aircraft (the launcher) are not designed for that. adding the strength to handle it means adding weight. Plus, it does not account for safety issues. You are carrying an orbiter craft fully loaded with humans and flammable fuel - what if the separation process fails? Having an escape tunnel back to the launcher is not feasible. An escape rocket like the ones on capsules means the left-over craft is a lot less aerodynamic, possibly unstable. You have to allow the possibility of landing without separation.

landing in crosswinds is typically handled for airliners with a simple rule… don’t. If the crosswind exceeds the limit, use a cross runway instead. There are two ways of dealing with crosswinds - bank to stay straight, or crab. The B52’s apparently had all steerable wheels, so it could land crabbed. Banking risks the wingtip striking.

Hooking up with the landing magnetic receiver is an unnecessary complication, adding the issue of more weight to put any magnets into the launch craft. You also underestimate the ease of mating two devices precisely travelling 500mph; and what then? It decelerates at a hard rate, what stops the launcher from sliding off the front of the sled?

A sled braking hard with a large load on top will tend to rotate forward, causing nose strike… Some serious engineering is required to prevent nose tipping. tailwheel aircraft always risked nose-over with heavy braking.

Most aircraft landing are going nose up to reduce speed. coming in hot has its own risks. Nose up, the craft will take several seconds to level off down once the read makes contact with the sled, eating up precious runway ; plus, how do you get the sled up to speed to match the incoming aircraft - it takes some serious distance to get up to 500mph even if it is capable of serious acceleration. 600mph is 10mi/minute or a mile every 6 seconds. the window to match speed, contact, lock and start to decelerate is pretty short. The shuttle allegedly had the aerodynamic qualities of a brick, and needed a 3 mile runway and a drag chute to stop.

All in all, vertical launch is the way to go. The Shuttle’s fatal flaw was mounting the shuttle on the side of the tank where it was susceptible to ice debris, instead of on top. IIRC, there has not been a case where the rocket failing killed the crew during any other vertical launches.

One suggested tech I saw (Heinlein? Clarke? Niven?) was to put a magnetic launcher running up a mountainside. The (unmanned) sled would be aerodynamic enough to glide down after the launch or use parachutes, the rocket would fire at the end of the run, you might get a few thousand mph and a few thousand feet of altitude to kickstart. Being just a sled, the launcher would not need fancy engines, or any maneuvering to avoid being blasted, or anything fancy like that - it would just drop away like the Shuttle solid fuel boosters, maybe a small perpendicular rocket blast from the sled to ensure separation. the only question would be how expensive a 30-mile track would be, how to build it on a tall mountain, and how much speed you could get out of it. Allegedly toward the end you would curve it toward vertical if you could to increase the effective launch profile.

17

This and similar concepts and issues have been discussed before many times on this and other forums. Some of these have been very detailed with lots of references. See below.

Re safety, when describing the forces and dynamics on the shuttle during initial powered ascent, astronaut Story Musgrave likened it to a “butterfly bolted onto a bullet”. It could withstand that – but only in a narrow range of attack angles. This was not unique to the shuttle – by necessity all launch vehicles must be extremely thin and light. They are only strong in the load paths required. This is why you rarely see partial launch vehicle failures – with buckled skin, trailing smoke like a WWII bomber as it limps into orbit. They either work near perfectly or the failures rapidly cascade to total destruction. This would be the case with any design, whether horizontal or vertical launch, mag-rail assisted, airbreathing or not.

In general the problem is an efficient two-stage fully reusable launcher must achieve a very high staging velocity (roughly around Mach 10), otherwise the upper stage is huge and combined vehicle weight is high. See graphs:

Prior similar discussions:

http://boards.straightdope.com/sdmb/showthread.php?p=20114485#post20114485

http://boards.straightdope.com/sdmb/showthread.php?p=19506732#post19506732

https://boards.straightdope.com/sdmb/showthread.php?p=21889103&posted=1#post21889103

18

That’s really the telling thing here. In your scheme, you’ll have a very complicated system to basically get yourself to about 50,000 feet and probably a few hundred knots before you launch, and it probably takes a good long while to get to that altitude, etc…

It’s probably a lot easier to just use solid rocket boosters- I’m willing to bet that by the time a more conventional rocket gets to 50,000 feet (~15 km), it’s going a whole lot faster than a few hundred knots.

19

Anyone interested in this might want to read Project HARP - Wikipedia. The High Altitude Research Project was an attempt to put objects in orbit using a great big gun. It got objects up as high as 180 km, but with only a quarter of the delta V needed for escape Of course, it could never have been used to put humans in space (deadly acceleration).

20

That is correct. The two main losses are “gravity loss” and “drag loss”. These are known for various launch systems and while significant, are not dominant.

E.g, LEO orbital velocity is about 8,000 meters per sec. Gravity loss on the space shuttle was about 1,222 m/s and drag loss was about 107 m/s, or about 16.7% total.

However raising the launch vehicle to 50,000 ft at a few hundred mph would not totally eliminate these, only reduce them. Even at 50k ft a launch vehicle is not totally horizontal, so it’s still accumulating gravity losses. Likewise there is still air drag at 50,000 ft, in fact that is close to the “Max Q” or greatest aerodynamic pressure for many ascent profiles.

As a wild guess if we assume the gravity and drag losses were cut by 1/2 or 2/3, that gigantic effort (and development expense) to lift a huge vehicle to that altitude by mother ship or magnetic rail would only save about 8-11% of the total delta V.