Human orbital spaceflight: the ultralight approach
by Richard Speck
|What if 215 kg (with astronaut) is the entire payload necessary for orbital spaceflight, including access to a space station and return? With today’s launch prices the flight cost could be under $2 million.|
At the core of “rocket science” lies the Rocket Equation: Delta V = Vexhaust*Ln (mass ratio). (This is the only equation in the article!) Now ignore everything but the term mass ratio. Spaceflight does not require large and expensive launch vehicles if the payload is small. For hydrocarbon fuels, the launch mass is 30 to 60 times the orbited payload. You can either make the launch system large or work hard to make the payload very lightweight. Production and development costs scale almost linearly with mass for many products, and will for entrepreneurial launch vehicles as well.
There are fixed-weight components. In 1958 a rocket guidance computer weighed about 90 kilograms, and this limited how light a system could be. A much more powerful computer today weighs less than a gram. The human is one fixed mass component (although in fact compact astronauts will have a large advantage).
What if 215 kg (with astronaut) is the entire payload necessary for orbital spaceflight, including access to a space station and return? With today’s launch prices the flight cost could be under $2 million. With modest progress (from today’s 1960 missile derivatives) the orbital ticket could be $200,000—conceivably in the next two years. Radical (and later) achievements bring this price down even farther. In fact the fuel necessary to fly one human to orbit with such a system equals the amount of gasoline most of us put in the family car in a single year! (Added to a larger amount of very low-cost liquid oxygen). I personally won’t wait for a $2,000 ticket price!
Micro-Space, Inc. is actively working to perfect lightweight systems for spaceflight to orbit, to the Moon, and to Mars. But for now, I want to discuss what “economy” personal spaceflight, in the next few years, might look like.
Forget exotic artist’s conceptions. This will largely be a combination of SCUBA-type gear, high-altitude mountaineering, and skydiving. Yes, you will land with a parachute, like thousands do for fun every weekend. Yes, you will need extensive training. Yes, there are risks.
With the lightest weight launch system you won’t actually be in a spacecraft: you will arrive in orbit attached to your recovery system. If anything goes wrong, you will be equipped to make a safe return at any time.
You will be instead be in your spacesuit. It will be soon demonstrated that redundant life support is feasible with mechanically-constrained spacesuits. Even triply-redundant systems will be feasible. A hole in your spacesuit is not a big problem, although it could result in local skin damage. The F-22 “Partial Pressure Suit” is a good example of this system. Although the user is encased in an anti G-garment and counterpressure vest, he is not sealed in an airtight envelope. Purely mechanical systems, even elastic bands, could serve as counterpressure systems with multiple redundancy and little chance for failure. The F-22 suit was chamber tested to 20 km altitude, where air pressure is only 5.5% of sea level. This is close enough to space to make little practical difference.
The face mask is the critical part. In the F-22 it is forced against the users face by an inflated air bladder and straps so that little of the positive pressure oxygen he is breathing leaks out. Air is forced into his lungs at a fraction of an atmosphere, and he can exhale against this pressure, with the counterpressure vest helping squeeze his chest. This vest also prevents overinflation of his lungs if he relaxes. Sealing the breathing connection is easier with SCUBA mouthpieces, but this makes talking difficult.
Life is easier with an air-filled helmet—the classic spacesuit helmet. But the simpler system could be worn inside such a helmet, just in case. The mask could be nearly indestructible with check valves and multiple oxygen supplies. A risk remains, but there is no need to make this safer than riding in your car!
|With the lightest weight launch system you won’t actually be in a spacecraft: you will arrive in orbit attached to your recovery system. You will be instead be in your spacesuit.|
A few observations are important. It is always pointed out that blood boils above 18,000 meters altitude. Yes, blood spilled on the floor and kept warm boils at this altitude, but blood spilled on the floor isn’t useful anyway! An exercising human has a blood pressure at least four times this vapor pressure, and if he doesn’t literally explode from this blood pressure, he won’t explode from this vapor pressure! The vapor pressure is 47 mm/Hg. The venous pressure in the feet of a tall man should be at least three times this large from hydrostatic pressure alone.
Actually, the human body is pretty tough. I have exposed spots on my hands to vacuum—a full 760 mm/Hg pressure differential—many times, placing them over tubes and pipes to check vacuum systems. If this pressure would tear up the human body, even OSHA-approved air guns and “Dust Off” cans would be stripping flesh off people every day! There is no need to deal with this pressure in spaceflight and many reasons not to.
Full pressure makes spacesuits almost useless. It makes explosive decompression a very traumatic event. And, if done with mixed gas—air—it guarantees potentially fatal decompression sickness even if the decompression occurs more slowly. Yes, the diver’s “bends” is a big problem with poorly-designed space systems, and makes preparing for an EVA a long and difficult process. Breathing oxygen has a long history in aircraft and spacecraft, and is used by mountain climbers and sick people on this planet. It is even used in moderation by divers. Beyond cautions that are easily avoided in space, it creates few medical problems. Some people may not tolerate it, just as some do not acclimate to altitude and some are killed by peanut butter. But oxygen tends to be avoided for other reasons.
Oxygen promotes combustion, making fires worse. Fire is, of course, a serious problem on this planet even without concentrated oxygen. The problem is reduced, but not eliminated, when cabin pressure is lower (and also lower in zero G). Presumably nearly-fireproof cabin systems can be designed. But until that is achieved, there is a well-known solution. If the humans present are already fitted with oxygen masks, flooding the cabin with carbon dioxide quickly ends any combustion with no damage to the equipment. Several Halon-like materials are also available which extinguish combustion even faster. In any case, these systems are good enough for me, and are incorporated in many race cars.
Back to your affordable spaceflight: you are in a safe pressure suit. You are protected by a “shroud” during atmospheric flight, just as satellites are. Humans are tougher than most satellites. When a satellite is exposed to the kind of stresses a Super Bowl quarterback regularly encounters, it takes months to repair. At about 50 km altitude you will no longer need protection from the wind blast, and the shroud is ejected to minimize its effect on the launch payload capacity.
Feeling as naked as a skier on a sky-high chair lift, you continue to accelerate. You have steady life support, are lashed into the acceleration seat in front of your reentry heat shield and have solid radio communication. But beyond your feet lies a large part of the planet. You will not wait to enjoy an unobstructed view—it comes early. If you did a good job cleaning your face mask, you will have a view with clarity, contrast, and color which can be captured by no camera! Eventually the elephant sitting on your chest will blow away with various grunts and whooshes: sounds conducted through the structure, not through space.
|Just as passenger submarines are being developed for those who want a taste of undersea exploration without effort, passenger spaceships will eventually offer flights to the wealthy. The risks for diving are much greater than those for ultralight spaceflight.|
Soon thereafter you should see your destination space station glowing against the black sky. You will know exactly where you are: GPS works even better in low Earth orbit than on the ground. Differential GPS, using data communication with the space station, will define your relative position, second by second, to a fraction of a centimeter. You are moving fast compared to the blue planet rolling past under your feet. But you seem to be drifting toward the station like a boat docking on a calm day. In actual fact, for all maneuvers done in less than fifteen minutes, you could be docking a boat, or putting your car in the garage. Gentle puffs from the maneuvering jets produce predictable small changes in velocity. You don’t have to actually do anything yourself. Someone on the station can observe, supervise, or guide your rendezvous, and this is a very easy process to automate. It was different when there was no GPS, no global communications, and computers were huge. But today, your PDA can handle the computations with a fraction of its capability.
When you arrive, to hang motionless near the space station, you will unbuckle. Your reentry unit stays hitched outside the station like the horses in an old western town. Newbies may actually be caught in a net, on which they can climb to the hatch, to avoid real “space diving”. Knock and wait for the door to be opened for you.
Eventually, you will be forced to go home. In your spacesuit again, you strap yourself back onto your reentry unit. Now you are more than a passenger, and a very careful checklist must be followed. Just as passenger submarines are being developed for those who want a taste of undersea exploration without effort, passenger spaceships will eventually offer flights to the wealthy. The millions who enjoy SCUBA diving now have to make more of an effort and learn to be careful. For the flights I am discussing, you will need to do the same. The risks for diving are much greater than those for ultralight spaceflight.
Your reentry system is primarily a lightweight plastic dish, two meters in diameter. You will still have your small maneuvering jets to align your system for reentry. A retro rocket will reintroduce you to normal gravity for several seconds, and then you wait. You can enjoy your last views of the Earth rolling by under your feet, or you can chat with your friends below. After twenty minutes, air drag builds up and your phone call ends. You will be enveloped in a ball of plasma as your meteoritic flight slows down. The plastic, ablative heat shields are very stable, and have never failed in manned spaceflight.
When the elephant goes home again, blue sky will appear above you and you need to think about your parachute. With no uncertainty about your position, and no lack of communication, you will plan your touchdown just as you did in skydiving practice! Only this time, you’ll be returning from the trip of a lifetime.