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63 votes
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In this iconic lunar orbit rendezvous photo of John Houbolt, why do arrows #5 and #6 point the "wrong" way?

They are burns, with the direction of the arrow roughly indicating the direction of thrust. Ascent Earth orbit insertion Trans-lunar injection Midcourse correction Lunar orbit insertion Burn to drop ...
Organic Marble's user avatar
31 votes
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Why was orbital rendezvous considered so controversial?

It wasn't a non-issue at all, it was a complex technological problem to solve. When the Apollo program was conceived space flight was still in its infancy, humans had been in orbit, just. Orbital ...
GdD's user avatar
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30 votes

Refueling a Mars mission on the way

Unfortunately sending propellant ahead to pick up on route will not help. The same amount of propellant will be needed regardless if both are accelerated together or separately. Also if launched ...
Slarty's user avatar
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29 votes
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Why was Apollo mission launched on one big rocket? Wouldn't rendezvous in earth orbit using a smaller rocket have been an easier challenge?

Assembling or fueling the Apollo spacecraft in Earth orbit from multiple smaller launches was considered; it's referred to as the Earth Orbit Rendezvous mission mode. The original EOR studies were ...
Russell Borogove's user avatar
28 votes

How will DART be able to hit a 170 meter rock dead-center at over 6000 m/s? What technologies will be use and how will they work together?

Didymos will be roughly 11 million kilometers (6.8 million miles) from Earth at the time of the DART impact.The round trip time for a radio signal from DART to the control center on Earth will be ...
Uwe's user avatar
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22 votes
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How did Soyuz MS-04 reach the ISS in only 6 hours?

On one of the Russian web sites there is an interview with Rafail Murtazin, deputy head of ballistics department of the Energia corporation, who is described as the developer of the expedited ...
mustaccio's user avatar
  • 492
20 votes

Why did rendezvous on Gemini 4 fail so badly?

Gemini 4 was the first unsuccessful try of a rendezvous. They sought at that times it should be possible to rendezvous from a short distance by simply thrusting towards the docking object. They had to ...
Uwe's user avatar
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19 votes
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Why did rendezvous on Gemini 4 fail so badly?

The long comment chain below this answer highlights the mis-conception that NASA astronauts as a whole did not understand the orbital mechanics of docking. As this comment points out, the mechanics ...
uhoh's user avatar
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19 votes

How was Apollo supposed to rendezvous in the case of a lunar abort?

Lower orbits are faster, higher is slower, so by adjusting orbit altitude you can get an orbit that gains or lags until you are in position do execute a Hohmann transfer. The orbit period is around ...
GremlinWranger's user avatar
19 votes

Refueling a Mars mission on the way

If you think less about fuel and more about the other amenities for a long distance mission, you are awfully close to the concept of a cycler. The basic idea is that you take a big vessel, on which ...
mlk's user avatar
  • 449
18 votes

How did Soyuz MS-04 reach the ISS in only 6 hours?

Russia has been using expedited rendezvous since 2012 with the uncrewed Progress and since 2013 with the crewed Soyuz. Expedited rendezvous is a huge bonus for a crewed vehicle. This is particularly ...
David Hammen's user avatar
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17 votes

Refueling a Mars mission on the way

The real problem is that, in space travel, your speed determines your trajectory, and therefore two objects can't follow the same trajectory at different velocities. Precisely, a faster interplanetary ...
armand's user avatar
  • 559
16 votes

How was Apollo supposed to rendezvous in the case of a lunar abort?

There were specific procedures for an abort at any time during the powered descent and after landing. The abort case at the planned time of landing (about 12 minutes after PDI) is covered in this ...
indy91's user avatar
  • 1,991
15 votes

Orbital Rendezvous vs Hohmann Transfer

Circular orbits at different altitudes require different speeds, so if you start with a radial separation, the spacecraft and station will tend to drift further apart unless they accelerate themselves ...
Russell Borogove's user avatar
14 votes

Why did rendezvous on Gemini 4 fail so badly?

First, the Gemini IV maneuver was station-keeping, not rendezvous. Since the target was the just-separated upper stage, the two spacecraft were already rendezvoused, and point-and-burn would have ...
Mark's user avatar
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13 votes

Why was orbital rendezvous considered so controversial?

In addition to the complexities of actually performing the docking there is the additional detail that the abort options are significantly reduced. If one always has the fuel for the return trip, one ...
PearsonArtPhoto's user avatar
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12 votes
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Worst damage incurred during a rendevouz or docking operation?

Yes ! During an experimental docking manœuvre, a Progress spacecraft crashed into Mir and rendered the Spektr module uninhabitable. On June 25, 1997, the Progress M-34 spacecraft crashed into ...
Antzi's user avatar
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11 votes
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Can someone give me a 'trajectory optimisation for dummies' answer?

I'm in search of a similar answer, so I thought I'd start one here and let others offer input. Here's what I've found so far. Reading list I'll start to compile some general links here. Books ...
Translunar's user avatar
  • 1,108
11 votes
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How important is plume impingement in rendezvous operations?

NOTE: My answer applies specifically to Space Shuttle (STS) operations. In general, it is quite safe to say that it is never desireable that the chaser plume the target to any significant degree ...
Digger's user avatar
  • 4,185
10 votes

Is there any kind of research on *sub*-orbital rendezvous-ing with a space tug outside the atmosphere?

I can't find anything on this online. It would seem to be a useful technique as it would lower the delta-v for the vehicle that lifts the payload from the ground to the rendezvous point relative to ...
Russell Borogove's user avatar
9 votes
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Has on-orbit refueling ever been demonstrated with cryogenic fuels?

No. (Unless it has been done as part of a secret mission.) NASA's Space Technology Mission Directorate had plans for just that called Cryogenic Propellant Storage & Transfer (CPST), which would ...
Mark Adler's user avatar
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9 votes
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How did mission control work for the concurrent Gemini 6A and 7 missions?

They didn't have two functioning control rooms, so swapped off using the control room for the vehicle that was most active at the time, and used the distributed Mercury-style control for the less ...
Organic Marble's user avatar
8 votes
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Did the astronauts of Gemini 4 have any realistic rendezvous simulator training of orbital mechanic effects?

Let my preface my answer with a quote from Wally Schirra after Gemini 6A: "Somebody said ... when you come to within three miles (5 km), you've rendezvoused. If anybody thinks they've pulled a ...
Digger's user avatar
  • 4,185
8 votes

Can someone give me a 'trajectory optimisation for dummies' answer?

In its broadest form, Trajectory Optimization is simply finding the best path (and control values to produce this path) that satisfy the dynamics. The dynamics, in this case, are either the orbital ...
Paul's user avatar
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8 votes

How will DART be able to hit a 170 meter rock dead-center at over 6000 m/s? What technologies will be use and how will they work together?

I don't work for NASA, so I don't know exactly what algorithm DART will use for its terminal guidance. But I do know that it doesn't need to be particularly complicated. DART has a high-resolution ...
Ilmari Karonen's user avatar
7 votes

Lunar lander reaching orbital velocity to dock with the orbiter for return to earth

The upper stage of the Apollo lunar landing module ("LM") is itself a complete rocket ship, with an engine, propellant tanks, small thrusters to steer with, a guidance computer, and all the other ...
Russell Borogove's user avatar
7 votes

Refueling a Mars mission on the way

Rather than having fuel tanks you meet on the way the better way would be preposition fuel tankers at the start and end of the trip i.e Earth and Mars orbit. You put fuel tankers in Earth's orbit as ...
Rob's user avatar
  • 200
7 votes
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How to keep the phase angle with an Hohmann transfer?

To see why a Hohmann transfer is applicable for a symmetric jump preserving phase angle, let's consider what the semi-major axis of the transfer ellipse is: $$a_{H} = \frac{periapsis_H + apoapsis_H}{2}...
SE - stop firing the good guys's user avatar
6 votes

Sparking/arcing distance between two spacecraft?

I'm unable to give you precise numbers, but for orders of 10kV this will be a sub-millimeter distance. The mechanism of arcing in vacuum is significantly different than in air. While in air the air ...
SF.'s user avatar
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6 votes
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Would an orbital scaffold or shipyard be useful?

It depends a lot on what capabilities this shipyard brings. One of the primary advantages could be in tremendous volume savings - by having a dedicated spot to do the majority of the spacecraft ...
fuchstraumer's user avatar

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