OpenSpace 4

Jump from space

Author: Mr. Giorgi Lobzhanidze

Address: Tbilisi, Republic of Georgia, Europe

Email: mailto:giorgi9@gmail.com

Introduction

The parachuting is considered to be one of the most attracting, exciting and wonderful kinds of sport. From the beginning of the twentieth century it has been adopted by pilots for safe flight and later it became breathtaking kind of sport. Throughout the previous century there were developed many kinds of it, such as:

• Accuracy landing - Landing as close as possible to a target.

• BASE jumping - From buildings, antennas, bridges (spans) and cliffs (earth).

• Blade running - A kind of slalom with parachute.

• Big-ways - Formation skydiving with many people.

• Canopy formations - Making formations with other parachutists while under canopies. (Known also as canopy relative work or simply CRW)

• Canopy piloting - Also known as 'swooping'.

• Formation skydiving - Making formations during freefall. (Known also as relative work or simply RW)

• Freefall cinematography

• Freefall style

• Freeflying

• Freestyle skydiving

• Military Parachuting

• HALO/HAHO

• Treejumping

• araski

• Skysurfing - Skydiving with a board strapped to your feet.

• Wingsuit flying - Skydiving with a suit which provides extra lift.

In spite of such great choice for sky divers there probably could be one more, perhaps the very unusual kind of this sport-jump from the space.

Typically, parachuting occurs at the altitude of 4000 meters where the air is enough for breathing. In principle there is no difficulty to increase this altitude (and hence the time spent in Free-Fall), probably the sky diver will need to carry oxygen mask and warm cloth. However, we think that the space parachuting will be completely different thing.

Generally, the atmosphere has got no clear boundary to space since the atmospheric pressure and density gradually decreases by growing altitude. However, according to the international definition the formal boundary lies at the altitude of 100 kilometers, therefore jump from space must be occurred at this altitude or a bit higher. Undoubtedly, such jump will require different conditions.

Achieving Altitude

First of all, no airplane, helicopter or the gondola of a balloon is able to carry passenger (sky diver) to such altitude, therefore a suborbital rocket/spacecraft will be needed, for example like the SpaceShipOne that has been recently used for winning the X-Prize in 2004 year, the other option implies using the Space Elevator (we discuss this option thoroughly below). A space-suit with some Oxygen supply (for at least 1-2 hours) will be also needed. The spacesuit must meet specific requirements since that altitude and acceleration 9.8 m/sec2 will cause the fact that the any object falling from such altitude will enter the atmosphere very quickly and this circumstance from its side will lead to heating object’s surface. Of course the temperature in this case will not be as high as in case of orbital entry. Here we are guiding by the manual written for the suborbital spacecrafts by Drs. Marti Sarigul-Klijn and Nesrin Sarigul-Klijn: “Flight Mechanics of Manned Sub-orbital Reusable Launch Vehicles with Recommendations for Launch and Recovery” ^{1 2} that shows the correlation between the maximum temperature and deceleration experienced during the descent. It concludes that maximal temperature will be about 540 ° by Celsius due to the Mach 3.5 entry. As for the maximal g-load during fall it reaches 5.5 g at 21.3 km altitude (however we should note that these values cold vary due to vehicle’s shape). We are convinced that this g-load 5.5 g will not make any serious problems since it will be tolerable for the trained jumper; we know that the candidates for spaceflight should withstand much more g-loads that occur at descent. Generally during the lift-off the astronauts have to bear not more than 3g's but this lasts several minutes until the spacecraft reaches the orbit. In our case it will last much shorter time and after all such extreme kind of sport as parachuting (especially space-parachuting) is for well-trained persons only.

Equipment

As for high temperature (540° by Celsius) it will definitely occur at such jump and needs to be solved since usually the spacesuits are not designed to withstand high temperatures. Generally, both g-load and temperature could be somehow controlled by means of falling in a vertical or horizontal position. In other words the sky diver can fall in vertical position-with legs directed downwards and hence the head directed upwards or horizontally. The sky divers generally do like this-control their velocity when falling down by means of attitude control. However these measurements can not completely solve the problem-the high temperature will occur during such cosmic parachuting.

We think that this problem can be solved by means of designing, manufacturing and using the heat-proof spacesuit meeting extreme requirements-it should withstand cosmic freeze and quite high temperature (540 ° by Celsius or a bit more) during cosmic parachuting. Simultaneously it must be quite elastic since the jumper will need to move his legs, hands and fingers more than astronaut generally needs during spaceflight. Besides, the spacesuit should be covered with additional outer layer that will protect the jumper from the heat generated due to atmospheric friction. Generally apparently this is not very difficult problem since the temperature is not very high and the fall will last only several minutes. In addition, if after the cosmic parachuting the splashdown is occurred in ocean the water will cool the spacesuit and the problem would be finally solved. Perhaps it will be found out that it is possible to use the already-existing spacesuits if they are covered with that additional outer layer meeting all necessary requirements.

As for the parachutes, they also should meet the specific requirements, actually two: they must be kept hermetically inside the spacesuit, besides the parachute should be quite large since the altitude at such jump is much more than in case of ordinary jump, in other words the velocity of falling will be more, hence large parachute will be needed for braking and the weight of the jumper is also more due to spacesuit.

One very specific problem may arise during such parachuting: there is possibility that jumper to begin spinning just after jump and this is undesirable since such spin may prevent the parachute to deploy if spinning is not stopped. Besides, continuous spin may cause sickness. Generally spinning may be stopped by means of dense atmospheric layers but at 100 km altitude there is no air and such somersault will prevent of getting the whole pleasure from such jump. Therefore, the jumper should be very careful in the beginning of jump; or he should have some device to stop spinning, for example some kind of gas pistol (like the one that sometimes is used during Extra Vehicular Activity) that will be fired against the spin direction and thus the spin will be mainly stopped. Of course, after entering the dense atmospheric layers there will be no problems, therefore this measurement is for the upper layers only.

To protect the cosmic jumper from high temperature we can apply to other measurement, perhaps quite unusual. The jumper may use some kind of heat-proof shield that he will hold in his hands during descending, the shield that will be directed downwards and will counteract the air. The parachutist during falling down should be very careful-the shield MUST be directed exactly downwards to avoid harmful influence of hot air. Also, it is better if the shield is transparent since the jumper will be able to see the Earth and the whole falling process below. After braking to the safe velocity and altitude where the spacesuit will not be heated the jumper may simply throw the shield away and continue falling down with spacesuit only. The shield itself may have flat or a bit curved shape, but it must cover the whole area of the spacesuit. We think that it is quite easy to choose the material for the shield and probably such approach for solving this problem would be justified. As for the weight of the shield it will not make any problem since both shield and jumper will be mainly in the state of weightlessness during falling down and the jumper will have to control his attitude only. Finally, we can conclude that designing such heat-proof shield will pave the way to the successful cosmic jump. As for the spacesuit itself it could be the same as used by astronauts nowadays and no special additional outer layer will be needed.

Taking into consideration all above-mentioned factors we can easily design such protective shield and execute very attractive and exciting kind of sport activity-jump from space. We think that designing the shield and thus accomplishing the jump from space will be apparently much easier than designing heat-proof spacesuit with its additional layer that should be thin enough (in case of thick layer the spacesuit would not be elastic); however we should not reject any of them since only the practice will show us which method is more suitable for space parachuting.

Protective Shield

Now, a bit more about the protective shield itself. What kind of shape should it have? To our mind the hemisphere shape will be the most suitable since it has got the simplest aerodynamic form, it will be easy for the jumper being inside to control his attitude-as we know the jumper must be always inside the protective shield, and if the shield is much heavier than jumper (this is desired) it will always be under the parachutist during falling down, and this is what we need. For guarantying precise and good descent the size of the shield should be a bit more than size of the jumper itself. In such case the shield will completely hold the jumper inside it. Apparently, the system shield-human after entering the dense atmospheric layers will be stable and its heavier part-the shield will be always under the human and its simple shape-the hemisphere will sustain this situation.

Also, we think that the shield should have several little winglets around it; they will act as stabilizer when the shield enters the atmosphere. This measurement will enable the system shield-human to fall in vertical position and not to somersault in air. This means that the extreme attention will be needed just in the beginning when the jumper still falls in vacuum since it is absolutely necessary that shield-human to enter the atmosphere vertically-shield directed downwards.

Will the protective shield be reusable or expendable? Well, it depends at what speed it will fall into the ocean at splashdown. As written above, at certain altitude the jumper will simply throw the shield away and continue descent with spacesuit only. The shield will keep falling down until colliding with water surface where it will be probably severely damaged (actually this also depends on the angles of collision. For instance if the shield collides with water from lateral side apparently the damage will be less) and will not be capable to be used again, however if it is equipped with its own parachute or retrorockets it would be possible to use it again.

But if it is turned out that parachuting with hemisphere shield is still very risky action due to problem with sustaining stability system shield-human then we will have to execute jump from space with complete sphere-shape shield. In this case the shield will have the shape of the ordinary sphere with hollowness inside where the jumper will be placed and it will be opened by the jumper from inside when necessary. Under such approach there will be no need of the gas pistol, we will not need to care about shield-human system stability and etc. The shield should be made of transparent material because the jumper will need to see the Earth. The falling process will be a bit simpler than in previous case: after separating from the suborbital spacecraft the sphere-shape shield and jumper inside may spin and it will not be possible to stop this rotation. At the certain altitude the jumper will open the shield and will continue falling down as in previous case.

As we see the jump from space is possible to execute in three different ways and the third one is the most comfortable and acceptable since it is the safest. However, to accept it as the best method for executing jumping from space, one formal circumstance makes a problem.

Why do we need to jump from space? The answer is clear-for setting new world record, for executing new kind of sport activity and not for descending from high altitudes itself as such since it has been executed from 1961 many times.

Let’s think about it-what would be the difference between descending from suborbital altitude with spacecraft and with above mentioned sphere-shaped shield? We can state that there would be no substantial difference since in both cases the jumper/astronaut will wear spacesuit and besides in addition he will be placed in the medium completely covering him and protecting from high temperature and vacuum. If we do not distinguish the sphere-shaped shield from the spacecraft on the grounds that both of them are the medium where the jumper/astronaut is placed hermetically and covering him completely then we should admit that jumping with sphere-shaped shield will be almost the same as descending with spacecraft and this has got nothing to do with parachuting at all.

Still, which circumstance should we consider as essential difference between descending from suborbital altitude with spacecraft and with parachute? We think that following two:

1. During the descent the jumper should NOT be covered with something else (except spacesuit of course) completely and hermetically, otherwise it will be descending inside the spacecraft and not parachuting.

2. During the descent the jumper should control the attitude with his body, legs, hands and fingers in order this process to be similar to an ordinary parachuting. Otherwise, it would be descending with ordinary spacecraft.

Therefore, based on the above written, we think that the best option for jumping from space would be the second method, jumping with hemisphere shield since exactly this enable the jumper to reveal his dexterity and courage during falling down and hence exactly this will be considered as the most extreme and attractive kind of parachuting.

Physics

Now, how such jump can be accomplished in practice? What kind of transportation system can be used for delivering the jumper from the Earth to suborbital altitude? We think that the Space Elevator, the hypothetical structure that as expected will be used in future for delivering the payloads to space could be actually used for this purpose since its cabin will be able to carry the jumper with the shield. But how the jumper can be released from the cabin and begin falling down to the Earth?

The problem of various aspects regarding the Space Elevator’s cabin’s ascending process is well studied now by scientists , it indicates that “as the cabin climbs, the elevator takes on a 1 degree lean, due to the top of the elevator traveling faster than the bottom around the Earth (Coriolis force)” ³.

This 1 degree lean would be very useful if any object released from the cabin fell exactly vertically (relative to Earth’s surface), this would guarantee gradual recede from the East-going cable, but unfortunately at the Low Earth Orbit the Space Elevator’s cable’s tangential velocity is more than Earth’s rotational speed, therefore any object released from the Space Elevator will fall down and a bit forward/eastwards also in order to outstrip the Space Elevator’s cable. This circumstance might raise the danger of colliding the jumper with cable and this is absolutely intolerable. How this problem can be solved to protect both cable and jumper? There are several possible ways:

1. When the cabin ascends along the cable the latter is bent due to Coriolis force but if the cabin is stopped then within several hours (this time span may actually vary significantly) the cable will become balanced (as it was before cabin’s ascent) and hence we can release the jumper-he will fly downwards and eastwards and will not cross the cable.

2. The jumper should be slightly pushed to the directions orthogonal relative to Earth’s rotational one-that is northwards or southwards. This will enable the jumper to fall not exactly towards Equator but a bit northwards/southwards while the Space Elevator’s cable is always located in equatorial flatness.

3. The jumper can begin falling down not exactly from cable’s vicinities but a bit aside from. In this case jumper’s trajectory will be curve gradually approaching to cable-in theory they would cross in Earth’s centre. For accomplishing this in practice it is better if the cabin is deployed on the cable northward/southwards since in this case there will be at least additional several meters (this will be cabin’s size) from the cable for beginning the descent. For improving the situation the cabin should have a special adjusted platform where the jumper will descend from.

Which method will guarantee the best descent and avoid any collision of jumper with cable? Here we will discuss all three methods’ advantages and disadvantages in order to find the best one.

What can we say about the first method? It will justify itself if cabin’s stop will not make some significant problems, particularly if balancing the cable (that is becoming straight again) is not found dangerous.

The second and third ways are similar in some manner, both implies avoiding to encounter with cable, however the second one needs some initial thrust and third one guarantees only keeping some minimal distance between jumper and cable. This would be enough if the Earth had got no atmosphere since any object’s descent process would follow celestial mechanic’s laws only, but due to atmosphere it will be relatively difficult to predict jumper’s exact place of splashdown, for example because of winds in atmosphere’s upper layers. So, due to this very circumstance we would better choose the second way that will guarantee the maximal recede from the cable and for this purpose some slight initial thrust will be needed which can be achieved by means of solid-fueled rockets. See the image below depicting such descent:

How much time will be needed for jumper to ascend to necessary altitude by means of Space Elevator? Since this structure is not built yet we cannot answer this question thoroughly, however if the cabin gains the speed of a very fast car or train of 300 km/h it will take less than 1 hour to reach 100 km altitude. Even in case if the actual speed is less (this in principle can occur since the current speed of the climbers at the space elevator games about 2 m/s (7.2 km/h)) it still will be easy for the jumper to stay inside the cabin and then leave it just before jumping.

References:

1. http://www.spacefuture.com/archive/flight_mechanics_of_manned_suborbital_reusable_launch_vehicles_with_recommendations_for_launch_and_recovery.shtml

2. http://mae.ucdavis.edu/faculty/sarigul/AIAA_2003_0909_revised_Sep03.pdf

3. http://en.wikipedia.org/wiki/Space_Elevator#Climbers