Spacecub Frequently Asked Questions


What is the Spacecub?

The Spacecub is a manned, suborbital rocket meant to be built, operated and flown by individual hobbyists. It is planned to be fully reusable and not to drop pieces of itself along the way. In many ways the Spacecub can be thought of as a fully reusable, manned version of the Viking rocket of the early '50's since it has the same basic performance and general capability.

With the exception of the computers and electronics, most of the features of the Spacecub are rather old technology. Most of the technical issues have been dealt with thirty or more years ago.

What are the numbers for the Spacecub?

The Spacecub will have the following dimensions:

          Length:                      10 m (33 ft)
          Span:                        8.4 m (28 ft)
          Height:                      4 m (13 ft)
          Empty weight:                990 kg
          Payload:                     100 kg
          T-O weight:                  7090 kg
          Maximum altitude reached:    313 km
          Maximum range:               974 km (at 124 km peak altitude)
                                       (altitude is traded for range
                                        to some extent)
          Maximum velocity at burnout: 2255 m/s (5125 mph, about Mach 8)
          Flight time:                 10-20 min

How much will the Spacecub cost?

We're aiming at keeping the cost of the Spacecub down to about $200,000 in kit form with a fully constructed version at perhaps twice that.

How many passengers will it carry?

The current version of the Spacecub is a single seat vehicle, but there is the possibility of a "stretched" two seat version. Also, there are plans to use the experience gained in the first Spacecub to design and build new vehicles with greater range, more passengers, and larger payload capacity.

Why is the Spacecub suborbital? Why not make an orbital vehicle?

It takes a speed of nearly 8000 m/s to make orbit. However, fighting gravity and shouldering aside the atmosphere uses power that makes the rocket require a velocity potential (a "delta v") of about 9500 m/s. With kerosene and oxygen as propellants the rocket would need 20 times as much propellant as the empty weight of the rocket. The suborbital Spacecub only makes a speed of 2250 m/s but fighting gravity and the atmosphere requires a "delta v" of about 4300 m/s. To do this the rocket needs fuel of _6_ times the rocket's empty mass. This is much, much easier to do than 20 times.

Have any been built or flown yet?


What does the Spacecub look like?

The current design has a cylindrical (tubular) main body seven meters (21') long. The nose is conical and two meters long with a rounded tip and rounded "shoulders" where it meets the main body. The rocket has swept wings with root chord of 4 meters and a tip chord of 1 meter with the trailing edges swept back to a point one meter behind the main body. The span is 10 meters (33'). There are two vertical fins, one dorsal and one ventral, swept, two meters in root chord, 1 meter tip and with trailing edges also swept back 1 meter. Tip to tip span of the vertical fins is 4 meters.

How does the Spacecub take off? Vertically or horizontally like an airplane?

The Spacecub both takes off and lands vertically. This means that some fuel must be reserved for landing. This also means that virtually any flat surface ten to fifteen meters across can serve as an emergency landing point.

What will the experience of flying the Spacecub be like?

The flight will start, with the Spacecub fueled and checked, with the pilot laying back in the seat, with the nose of the Spacecub pointed at the sky. Mist, visible through the Spacecub's canopy, will drift around the front half of the Spacecub, condensation around the craft's liquid oxygen tank.

Then the engines will light. The engine's roar will shake the cockpit as the Spacecub begins to climb slowly into the sky. Acceleration will be gentle, a slight heaviness at first that will slowly increase until the pilot feels three times his own weight. In just over two minutes the Spacecub is over twelve miles up and breaking through the sound barrier. The engine noise vanishes and all becomes quiet.

Outside the sky becomes darker, first purple, then black. The stars become visible against the black.

Then, the engines cut out, less than four minutes after launch. All feeling of weight vanishes as the Spacecub begins its ballistic arc. For the next two minutes the Spacecub continues to coast upward before the ever-present pull of gravity begins to drag it back down. Then three minutes of falling and the rocket's wings begin to again feel the bite of the atmosphere. The air around the Spacecub begins to glow with heat. The skin of the Spacecub begins to warm as acceleration builds. The airflow over the wings generates lift, and the Spacecub starts to pull up from its dive. At an altitude of more than 20 miles the Spacecub comes level, still moving more than 3 times the speed of sound. The Spacecub slows, shedding energy and begins a gentle descent. At about 12 miles it drops back through the speed of sound.

The Spacecub glides to the landing target and pulls up in an increasingly steep climb. When it comes vertical the engines light and the Spacecub sinks vertically on its tail.

Why not use a parachute for landing, like the old Space Capsules?

Those old capsules set down at sea for a reason. Landing a large vehicle by parachute is hard on anyone in it. Such landings can end in broken bones and internal injuries.

Well, why not a horizontal landing, like an airplane?

The Spacecub would have a landing speed of nearly 200 miles an hour, and a power-off sink rate like a free-falling rock. That combination would make for a difficult and dangerous landing, far beyond the ability of most pilots. The Spacecub is aimed at hobbyists and pilots with a moderate amount of experience, not highly trained and experienced jet pilots.

How much does fuel cost for each flight?

A flight of maximum performance requires 360 gallons of kerosene and 660 gallons of liquid oxygen. With kerosene at $1.00 per gallon and the price of liquid oxygen as quoted by a local supplier of $0.35 per gallon a fully fueled flight would require $591.

How many flights will the Spacecub be able to make overall?

With regular inspections of flight critical hardware and occasional overhauls of the engines, just as on aircraft, there's no particular reason the Spacecub cannot last for years and hundreds, or thousands of flights.

What preparations are needed to fly the Spacecub again?

The Spacecub will require refueling, recharging of the batteries, resupply of the pressurized helium tanks, and a preflight checkout taking no more than an hour or so to be ready to fly again. This is an off the cuff estimate, though, until we actually have flight experience with the vehicle.

What kind of kit will the Spacecub be?

As presently conceived the Spacecub will be available in a "materials and components" kit. Actuators, sensors, engines, and complex parts such as those containing compound curves will be pre formed. The rest will be bar stock, sheet metal, etc., which will be cut and shaped by the builder.

What kind of materials will the Spacecub be made of?

The Spacecub uses mostly aluminum and titanium in its structure. The propellant tanks are sheet aluminum. The tank support structure is aluminum. The skin and skin support structure is titanium. Should titanium prove to be untenable, it would be possible to use steel instead, but the result would be either a more fragile vehicle (thinner skin and framing members) or a heavier vehicle, or both. Either result would reduce the performance of the spacecraft.

What will be used for reentry heat shielding?

At the speeds of the Spacecub, its size, and its mass, the skin of of the vehicle itself is adequate to survive reentry. The maximum temperature of the craft is less than 1000 K (1340 F).

What kind of redundancy will the Spacecub have? How will you handle an engine out on landing?

The Spacecub is designed to have three or four (not yet finalized) engines. The rocket engines we are looking at are the verniers from the Russian RD-107 or RD-108 engines. These engines have been around since the days of Sputnik and have established a simply incredible reliability. In addition, if _four_ are used then the Spacecub will have a full engine out capability--the ability to fly a complete trip with one engine out. (However, that ability comes at the cost of greater weight, and therefore loss of performance.) In the landing phase, the rocket has shed enough mass that any one engine is sufficient for landing.

Control systems and electronics will be fully redundant, with nice, simple, foolproof mechanical switches for shifting from main to backup systems.

How automated will the Spacecub be? Will the pilot be able to take control?

The Spacecub is designed so that the entire flight with the pilot doing no more than pushing the "go" switch, or with the computer doing nothing but provide data to the pilot who controls the entire flight manually, or any level of automation in between. This will allow pilots with a wide variety of different abilities and experiences to fly the Spacecub. At low levels the Spacecub would operate in a highly automated mode. As the pilot gains experience, the level of automation could be dropped until the pilot is flying manually.

What kind of license will be required to fly the Spacecub?

This is one of a number of yet unresolved legal issues. Current US law requires _each flight_ of a space vehicle to be licensed by the US Secretary of Commerce, in a process that can take up to six months. Not only the vehicle must be licensed, but the payload, and the launch site.

Currently, there is work underway to get these restrictions changed and to get a licensing procedure based loosely on aviation regulations enacted which will allow Certificates of Flightworthiness and Spacecraft Pilot's licenses which will let you file a flight plan and go.

The level I have been recommending for piloting the Spacecub is 250 hours of flight time, instrument, multi-engine, and aerobatic ratings.

Will the FAA allow the Spacecub to be launched?

Public Law 98-575, formerly HR 3942, gives the Secretary of Commerce _sole_ authority for the launch of all space objects (other than by the government or those acting on behalf of the government). This includes the launch of suborbital vehicles such as the Spacecub. Thus, the FAA does not seem to have jurisdiction on the matter.

What kind of launch and landing sites will be required?

The Spacecub needs a solid surface to launch from, a supply of liquid oxygen and kerosene (which can be trucked in), compressed helium, and a supply of electrical power to charge batteries. No specialized gantries, launch pads, or other such facilities will be required.

For landing, you need a flat spot to set it down, although it might be nice to have the facilities to take off again. :)

What is the liability exposure of the Spacecub?

This is an issue for the lawyers to wrangle over. The actual risk factor (to anyone but the pilot within the vehicle) is actually quite low. The total amount of fuel is 360 gallons, more than most lightplanes, but less than even corporate jets. The fuel we are considering is the low volatility Jet A, or JP-5 (military version of the same stuff) so even a complete, catastrophic failure of the fully fueled rocket on takeoff would be less disastrous than a similar failure in a corporate jet. Further, the terminal velocity of the falling rocket in the lower atmosphere is about 300 mph, and the rocket is quite lightweight at that point so a total failure here is limited in extent. Finally, the redundancy and engine out capability of the ship makes the occurrence of such a complete and total failure (or explosion) a very low likelihood event. In practical terms the rocket is no more hazardous, to bystanders, than aircraft of similar fuel capacity.

What environmental effects will a launch cause?

This was one of the reasons for the choice of propellants for the rocket: kerosene and oxygen. This was to avoid highly corrosive and toxic propellants such as hydrazine or Red Fuming Nitric Acid. The environmental effect would be that of burning 360 gallons of kerosene.

What about damage to the launch site from the rocket exhaust?

This is still an unknown. While the rocket exhaust is very hot, the total mass and exposure time is low. One trick under consideration for protection of the launch surface is to have the Spacecub carry a small water tank that sprays water into the exhaust to carry off the heat. About 120 gallons of water would be enough to carry off all the heat generated in the first ten seconds of flight. After that, the rocket is more than 100 meters up and no longer a danger to the surface below.

What about noise problems on launch and landing?

This is another unanswered question. The reputation rockets have for being really _loud_ comes from the big rockets people are most familiar with. For instance, the Atlas rocket has about 400,000 lbs or thrust on takeoff. The Spacecub has 20,000 lbs or thrust or so on takeoff. The bigger the rocket, the noisier. Just how loud the Spacecub will be is still not known though.

What international treaties affect the Spacecub?

This is another sticky issue. The main treaties are the 1967 Outer Space Treaty and the 1972 Convention of International Liability for Damage Caused by Space Objects. However, most of the provisions of these treaties can be neatly avoided by simply restricting flights to over the US. Flights to higher altitude will also need some check to avoid any risk of collision, yet such a risk is minute for the altitudes and flight times of the Spacecub.

Why would someone want to buy or use a Spacecub?

If one needs a "practical" reason the Spacecub is the fastest means of going up to 900 km. However, "practical" reasons aren't really what the Spacecub is about. It's meant for recreational flying. In the Spacecub one could see the sun against a black backdrop. One could experience weightlessness. One could see the Earth from above its atmosphere.

What about emergency considerations? Can the pilot extract himself from the rocket in an emergency?

In most possible failure modes, the pilot would be best advised to stay with the rocket. In particular, the pilot would _have_ to stay with the rocket at supersonic or extraatmospheric flight. The multiple engines provide the ability to the Spacecub to continue flying and either abort to a controlled landing or complete the flight even should an engine fail.

The prototype, however, will probably have some sort of escape system.

Perhaps the most serious potential problem for pilot safety is loss of cabin pressurization. As a shield against this a look is being taken at the Space Activity Suit, a skintight elastic garment that provides pressurization by direct pressure of the fabric. The suit has been tested to pressures of at least 2 psi and appears to be adequate for emergency use until reentering the lower atmosphere.

How can I find out more?

One way is to join the computer network GEnie. An ongoing discussion takes place there, including much of the work of designing the Spacecub. Another would be to send Email to David L. Burkhead on the Internet and ask to be on the Spacecub mailing list.

Any questions and comments would be most appreciated.

               David L. Burkhead