To the ballistic future: what is subborital trajectories and how spacecraft will fly on them
December 20, 2019 the launch of the American spacecraft CST-100 Starliner (Crew Space Transportation) of Boeing Development. The first flight came out abnormal, but not an emergency. After two days, the device successfully landed at the White Sands polygon. Nothing special, start like start.
By the method of Shuttle
However, in the ballistics of this and further launches of the "Starliner" there is a feature. The rocket displays it not to the space orbit, but on the subborobitative trajectory. Forms such a trajectory of the second stage – the oxygen-hydrogen grandfather "Centaur", a real cosmic locomotive, driven by the power of water vapor. The target orbit for which he delivers Starliner, with a cosmic apartment height of 188 km gets periya height 73 km. This is an atmosphere. If "StarLinener" will pass such perigee, he will fall. Therefore, after separation from the "Centauri" on the subborital trajectory, the ship is reproduced to enter the orbit 40-second incorporation of own engines.
This scheme ballistically repeats the removal of Space Shuttle, which launched solid fuel accelerators and its main engines to the Suverbital Curve. There, the shuttle dropped the fuel tank, flying along this trajectory until the entrance to the atmosphere, and passed to space orbit using orbital maneuvering engines.
Starliner copies the ballistics of the shuttle until its engines are turned on 30 minutes after the start. And the exhaust "Centaur" rolled into the ocean on the subborital trajectory, which he formed himself and the ship.
Path inside the Earth
Why "Starline" these tricks with a subborital trajectory? Such trajectories are of different forms, but everyone has a single ballistic basis – the ellipse of the orbital circulation of the body around the center of the mass of the Earth. And according to the equation of motion, and in its essence. These ellipses partially undergo under the surface of the planet, crossing it at points, which when driving a body in such an orbit become points of entry (fall) and output (start). Part of the orbit above the surface of the Earth is called a subborital trajectory. The body on it should not make a complete real turn.
Otherwise, subborital trajectories differ markedly. So, the warheads of intercontinental missiles of a large range rise by hundreds of kilometers per atmosphere, but having underground perigee, enter the dense layers with a decent tilt angle – 10-20 degrees to the horizon. What depth to go to the ground perigee and where exactly the issue of calculating such trajectories.
The second stage takes from the first elliptical movement with perichem deep into the mantle of the planet. Her task is to remove the perigee on the surface and further into space, for the desired height. According to the planned level of lift it is easy to estimate the required energy, the operation of the stage, the amount of fuel, the flight time on the main line and other parameters. The second stage "inflates" around the Earth, the subborobitative trajectory obtained from the first, lifting peria from the depths. The height on which to stop the rise is determined by the engine shutdown command.
Flight Dynamics Specialists chose a height of 73 km. But if perigee is needed in dense layers, why not leave it in the lower stratosphere, at an altitude of 15-20 km? And why immediately do not withdraw it beyond the atmosphere, having received a completely space orbit?
What are the versions?
To begin with, it can be assumed that the height of the perigete allows to reduce the stock of fuel in the ship. The higher Perigee, the mortar speed is needed to raise it into space to a given height. But why then perigee in the atmosphere? Technical resonances are possible – for example, eliminate the exit to emergency space orbits with an unacceptably long stay on them (which is bad for the crew, and for batteries). If this is not an orbit, the ship will enter the dense layers in the emergency compartment, and his return will be quite regular. So, with some failures, the subborital trajectory will automatically provide a normal landing.
Like the second stage, which set the atmospheric perigee is 73 km, will approach him in reality? With low apogee, 188 km, both points across the planet are minorly. In them, the orbit practically coincides in curvature from the earth itself. The trajectory in the Male-Growth of the Pergeus almost horizontal; The angles of its inclination – order of degree, and even then at the edges of the zone where they are always more. The step, very hollowing, will slow down the very top of the atmosphere for a long time, while not accumulating the reduction energy, aspiring to zero in the surroundings of the perige. Gradually increasing aerodynamics summarizes the braking of the device. As a result, the stage and landing apparatus will so much the speed that will not reach the perigue hundreds of kilometers.
Too stretched braking gives a greater dispersion of landing points. Why ask so much horizontal plot? With a perilem in 1000 km under the ground, the slope will be greater, the braking is more intense and shorter, and the scatter of the appearance of the fall is less.
With concern about people
The meaning of the Supportal trajectory of the removal of the pilotable ship is to reduce the overload in the emergency entry into the atmosphere. It is important for six people on board. A small overload exceeding our familiar doubles is easily transferred to people of any age and health status – this arises, for example, on American slides and does not harm the riding. With today’s emergency starts, the ballistic entry is much tougher, overload reaches 6-8 g. It is quite ordinary flight conditions, but only for trained pilots.
Overload happened and much stronger. So, when Falling "Union-18/1" on April 5, 1975, Vasily Lazarev and Oleg Makarov experienced more than 21 g. The upper point of the emergency trajectory came to a height of 192 km, from where the ship rushed to the atmosphere. The vertical component of the speed turned out to be big and tilt the angle of input down. Rappation with the bottom layers was rapid. The accumulated energy of the fall, even spending on the resistance of the air, easily maintained high speed to the most dense layers in which aerodynamic resistance increased tenfold. As a result of the combination of "High Speed - Dense Layers", braking was very strong, from the overloading, even the trained crew almost died.
In order to prevent such an intensity of entry in the accident, the second stage stretches the path of air braking of the payload, spending in the area of the perigeuy trajectory almost (and in perigue items) horizontally through the upper layers of the atmosphere. Lower the perigee into the atmosphere for such a depth so that overloads do not exceed the pairs of units, a simple computational task. The ship in the scenarios of the emergency separation from the stage moves along a similar trajectory.
Even if the stage has worked fine, critical failures may occur on the ship when in order to finally in orbit. This is a dangerous situation, which means that it needs to quickly plant.
Here, too, an emergency trajectory is useful with strongly stretched in time and therefore weakened overloads.
On the threshold of the epoch
In some sense, everything described is a step to the future passenger ballistics. Suppose Ilon Mask – or not a mask, and someone else will create a device transporting a hundred passengers at once. In this case, you will need to provide people with maximum comfort.
Military landing will join passenger ballistics. The big suburbital bus, it is only for him to appear, everything will be needed. Specifications will begin to be used to use. Perhaps combat landing ballistics will become, like aviation, to develop from military transportation subborital ballistics, initially unpilotable.
Supportal rocket will be useful, for example, to deliver cargo from Floridian Cape Canaveral to Afghanistan, on the American military base in the Bagram (orthodromic range of about 14 170 km). The main American military aircraft Boeing C-17 Globemaster III for delivery of typical 80 tons now need more than 15 hours of flight. In addition, the subborital path does not require permits for the span through national airspaces, allocating air corridors and bypassing thunder fronts. The first trials on the project are scheduled for the next year.
Forecasting the growth of the number of flights of new space technology, it is worth remembering that emergency launches will always be avoiding them. Ballistic suburbant tools are complex technical devices and complexes, and the failures in them are quite likely. But people on board should not experience significant overloads. It is in this direction that the idea is now developing.