Direct Ascent and Docking to Space Station Project
by Janez Vidmar (DocHoliday)

1. Project Concept

What we are trying to achieve is best described graphically, so make note of this diagram. It will be the guiding idea of this whole endevour.

2. A Sample Orbiter Addon Package

In the sample Addon pack provided, you take on the role of an experienced pilot astronaut, that is given the task to reach the MSS (Medical Space Station) in time to prevent an astronaut in EVA to lose his oxygen supply and die. The astronaut is unconscious, floating near the MSS, the skeleton crew of which can do nothing but watch and wait for your arrival.

You will be flying a DeltaGliderIII ready for launch sitting on a pad at Cape Canaveral and facing the proper launch direction of 42°, which will be later corrected to 47° by the flight computer so leave it as it is. For this emergency you are allowed to take off directly, without using the runway and without having to hover from the pad first before engaging main engines. You may, this once, just push the pedal to the metal when the time is right.

You must reach the helpless astronaut within 50 minutes, before his oxygen supply runs out. Remember what you learned, pay attention to the inflight instructions and keep your mind focused on the task. Good luck!

DOWNLOAD (Alpha Version) [Accessed 1162 time(s)]
DRAFT of the voice script (Excel table) [Accessed 76 time(s)]

A cockpit with a view!

Can you get to the astronaut in less than 40 minutes?

3. Steps needed to create a Direct Ascent and Docking Project

a. Define the Ascent Program parameters for the DGIII flight computer. Make sure the program gets you to the right altitude for you to intercept the orbiting target and consumes a miminum of fuel required to achieve the circular orbit at that altitude. There are many possible trajectories and any that brings you into an orbit of acceptable parameters at a decent fuel costs will do. Although calculation of the required pitch attitudes by altitude is no doubt possible, I suspect it to be so complex, as to become unpractical for our rather unexact needs.

b. Define the Launch Azimuth best suited for your needs. Roughly two options for a launch azimuth needed by the flight computer are possible. If you are skilled in math you can calculate it otherwise it is by trial and error. Not something one is liable to do in real life in such cases.

  • First approach is to achieve orbit and to perform MECO at the closest point to the targeted object. This method is the fastest, however costs insane amounts of fuel to cancel out the velocity acquired during the Ascent stage. Most of this counter velocity will be vectored to bring the relative inclination (RInc) of the two orbits to 0°. The proper timing is also hard to calculate and/or judge. Also the target starts to move away rapidly after closest distance has been achieved and there is little margin for error.
  • The second approach is to set your launch azimuth to minimize the distance the two craft will have at plane intersection point (in this case the Ascending Node -AN). At that point you are able to both perform the retro burn to decrease relative velocity with regard to the target object AND at the same time cancel our the relative inclination you have failed or were unable to cancel out during the ascent. It is quite common that the two burns are similar if not identical in direction and magnitude, which makes this approach a lot more appealing and fuel efficient. The object passes by the vessel in a much slower manner and also moves away, once closest distance has been achieved in much slower and more controllable manner. I recommend this approach as it is more predictable and reliable.

c. Define the launch window that enables you to pass the target at the closest possible range, so you have less to do after your finish your retro burn and find yourself in a static position with regard to the target. Again sequential testing is needed if you lack the proper mathematical expertise.

I hope you have as much fun with the Direct Approach as I have had making and testing it.

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