XAP (eXtreme Altitude Project) is a proposed combination of new technology for a somewhat revolutionary approach to ultra high manned balloon ascensions.

The existing FAI recognized Official Altitude Record for manned balloon flight is 113,000 feet. The unofficial record is 123,000, but without aerostatic return to a controlled landing. The officially recognized maximum altitude for heavier than air aircraft in level flight is held by the Blackbird at 85,000 feet. The Russian "Foxbat", has been to 123,524 feet.

The X-15 flights have been much higher, but only in short ballistic flights. Spacecraft, of course, routinely pass beyond this order of altitude penetration but cannot maintain altitude except in orbit.

Manned stable flight in the range between 125,000 feet and orbit has not been demonstrated.

XAP proposes extended duration flight between 125,000 and 160,000.

Our evaluation of the XAP proposal brings us to the opinion that it is now practical to proceed with this capability. It is considered that there is strong interest in the scientific and space technology communities for this facility.

XAP, however, has the philosophical problem that in one step it draws on several new and as yet unproven concepts and inventions. Each one is easily validated. XAP believes that the combination can be validated and routinely qualified for extended manned flights in the mesosphere.

High altitude balloon flight encounters logarithmic resistance with altitude. High altitude balloons become very big in relation to their launch gas volume. Extreme high altitude balloons soon reach the point of diminishing return with untenable skin surface in proportion to the gas bubble. At lower altitudes these balloons concentrate their lifting force in a proportionally small bubble in relation to the weight of the unsupported skin. Various means have been utilized to mitigate this phenomenon such as tailored shape and load tensors in the skin.

Small loads have been carried to the XAP target altitudes with some rate of success.

A second problem with existing technology is the duration of the inflation/launch window. Inflated balloons cannot be held for any appreciable time waiting for suitable launch conditions.

A third problem is the sudden release of the gas bubble and consequent dynamic loading of the bulk of the envelope skin.

Fourth is the addition of the payload to the already stressed balloon. As the balloon rises and the lifting gas expands the load is distributed and the strain decreases. The early climb is a critical phase. At lower altitudes the air is denser so this makes the greatest stress on the balloons.

Fifth, we note that cluster balloon systems have exhibited aerodynamic problems during climb to altitude caused by interrelation of the aerodynamics of the array.. This was one of the main reasons given for the termination of the Office of Naval Research’s Project Helios, the first plastic balloon project which initiated the whole field of the current balloon technology. (The safety of redundant balloon cell aerostats is a desirable given.) As a cluster of "Natural Shape" balloons rises, the air between the cells tends to be carried along with the balloons because of drag. The air outside of the cluster therefore has a higher differential with the balloons. The Bernoulli principal then draws the balloons apart which increases the effect. As a natural shape balloon moves a little off the airstream the non-inflated part of the balloon distends in the manner of a spinnaker sail and the balloon deviates even more from the system path to the point of laying out horizontally, creating insurmountable resistance. (The non-inflated part of the balloon which is tailored as an approximate sphere, collapses to a double wall spinnaker form and catches the relative air flow.) Multiple celled balloon systems have therefore categorically been deemed unworkable by the industry.

Sixth, the sudden release at launch in current procedures creates severe shock loads. These are generally manageable with normal systems.

Seventh, but not the least, is that the descent of a gas balloon from altitudes above 100,000 feet becomes uncontrollable because of the ratio of the adiabatic lapse rate of the lifting gas to the standing temperature gradient in the atmosphere. One cannot carry enough sand ballast to control the descent. This explains why stratosphere balloonists prefer water landings. At the altitudes envisioned by XAP even water landings will not provide relief from this natural physical fact.

The primary new invention for XAP is the "Tubular Gore Tetroon" (TGT). This spreads the lifting gas out over the whole skin of the balloon at launch and can then only start to inflate the main cell of the balloon as the system climbs. In its simplest form the TGT has only half of its gas in the main cavity at approximately 20,000 feet. More complex versions can be arranged to only start the main inflation at 30,000 to 40,000 feet altitude where the unit load is a fraction of that at sea level.

With the lifting gas distributed over the full surface of the tetroon each balloon can be contained in a shroud for extended periods and be released without the shock load. XAP has demonstrated that a TGT will exit from a protective shroud slowly and smoothly. Therefore we can pre-inflate the cells and retain them under protective air supported building style shrouds almost indefinitely waiting for a favorable launch window.

When the BGT is released from the shroud there is no shock load as the lift is distributed over the skin. This is in distinction from the orthodox plastic balloon launch where a bubble is released which lurches up to grab the weight of the rest of the balloon. At the start it exhibits hundreds or even thousands of pounds of free lift.

In order to minimize the load on the gas balloons at low altitude, where the unit lift of gas is high, XAP uses a manually controlled hot air balloon rigged between the BGTs and the payload. It supports the major portion of the payload module. As the system passes through the 500 milibar level the hot air balloon phase ends and the balloon deflates to a draped condition.

Partially inflated tetroons do not form spinnakers in windy conditions. The non-inflated portion below the bubble is more like a kite tail than a spinnaker. The BGT also does not spinnaker in the wind or in a divergent attitude in a cluster. It is more like an air mattress with non-inflated portions so it has more resistance but no sail. Early tests have shown that the TGT, when in the gore only inflated state, climbs smoothly at a reduced rate. That reduced rate tendency is compensated by the lift of the hot air balloon.

For controlled descent and soft touchdown XAP will utilize the hot air tow balloon. Tests have shown that a hot air balloon will readily inflate with ram air on descent. The hot air balloon segment of XAP has a stiff mouth to assist in smooth early inflation for a parachute style descent to lower altitudes where the air can be heated. Final stages of the flight are easily controlled by the hot air balloon. The gas cells can be completely deflated and/or released and destroyed prior to final touchdown.

It is recognized that some of these concepts are completely new and untested while others do have some precedents. Even though the XAP organization is confidant that the conglomeration of new systems will work together, it is accepted that development and progressive testing must be done by computer models, individual field tests and an extensive program of actual unmanned and manned flight demonstrations.

Rigorous analysis of the structure indicates that XAP is within the ability of the current state of the art for fabrication.

A normal "Natural shape" plastic balloon is fabricated from a multiplicity of individual sections. These sections are lenticular in shape, similar to meridianal orange peel sections. The TGT, or any tetrahedral shaped balloon (called "Tetroon" after Bill Huch), can be fabricated using one spiral gore. A tetrahedron is formed when a cylinder is sealed at each end with the end seals skewed at right angles to each other. An equilateral tetrahedron is formed when the distance between each seal end is equal. That distance mathematically is a little longer than the length of the cylinder which is, in fact, the altitude of one of the triangles described.

The TGT is formed from one gore. That gore can be a simple tube, a tube and parallel conjoined flat web or even two or more tubes and separating webs. In the multiple tube (but still single gore) conformation the tubes are connected serially. Only the first one is inflated at launch. The others inflate progressively as the balloon rises. Only after the final tube is completely inflated does gas spill over into the central cavity. As it progresses the tubes totally deflate and the central cavity takes its full volume form.

An important limiting design factor is the hoop stress in the tube at the top of the system at the start caused by the pressure head of the gas in the tube. This stress diminishes as the balloon climbs. Mathematical analysis indicates that several available balloon films are suitable and will be able to withstand the calculated stress.

XAP proposes a novel solution to the problem of extreme altitude research. Each facet is completely feasible. The successful combination of all these new concepts in one project will require superior coordination, but it appears to be well within this projected state of the art to accomplish the project at workable cost. Mesospherical balloon flight is attainable. We give it a Thumbs Up!