Pioneer - Get Ready for Launch!

rinku said:
Neal Stephenson's Seveneves is another one to read for this genre...
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I liked that for the first 50 to 60% of the book then he went in a very.... non-scientific 'change things to make a story' sort of way.
Fully agree that the first part of the book seems to fit the Pioneer theme well.
 
It's a book of two halves, but the second part happens a fair bit later and is probably in more traditional Traveller territory. Although it remains pretty hard science. The whole using whip dynamics for orbital transfer was apparently worked out properly.
 
What I disliked about the ending is the planet has all the water boiled away, oh wait there is water deep enough to keep a submarine working for hundreds of years, oh we can live in caves for hundreds of years as the atmosphere burns, etc. We have tens of thousands of people living in space stations all looking down on the planet but no one ever noticed .... they are nice story lines but extremely hard to believe.
 
I'm not sure that's exactly how it went, but it's been a while since I read it.
Regarding the oceans... they may have lowered but I don't think they went anywhere near totally evaporating, Battleship Yamato style.
Edit: Nope, he went there. However that process took a long while, and the Pingers INITIALLY sheltered in underwater caves, only later emerging after things had cooled down and gotten wet again. I doubt the spacers would have had to do more than top up the oceans with cometary water too... even if it escapes as steam it rapidly cools off and forms water and ice. Essentially you'll get some loss to space, but most of it is coming back down eventually.
 
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P-Minus 1 Day.

We are all prepped on the launch pad, and the Pioneer RPG is set to launch on Kickstarter tomorrow!

Get ready to explore the Solar System in a timeline very near our own and advance the goals of science.


Countdown Graphic P-1.png

Get ready for launch at 2pm GMT tomorrow!

And there will be a free 92-page preview to download, with Pioneer creation, the core rules, and a complete mission to get you started and into space...
 
robertsconley said:
For folks who may be interested in this stuff.

Maneuver Plans​

For delta-vee maneuvers, you will need a plan of maneuvers (burns) to get from where you are now to where you want to be. Unlike most vehicles, you are not concerned with how long you can move for. Rather, you are concerned with how much you can change your velocity by. This is represented by how much of the total mass your craft is fuel (the mass ratio), how efficient your engines are (ISP/exhaust velocity) are. What this gets you in the end is a number called delta-vee, rated in meters per second.

If you start out in a 250km orbit around the earth, and if you have roughly 4,000 m/sec delta vee of fuel left in your craft. You will be able to head out to the moon and settle into a 100km orbit. Around 3,100 m/s will need to be burned while you are in Earth orbit, and the rest when you enter the moon's sphere of influence and burn at the right time.

However, for an RPG campaign, you don't need to do the actual trajectory calculations. What you need is the total energy the trip will take and a good estimate of how long it will take.

If you're talking about a three-body situation like the sun-earth-mars. If you want to be accurate without doing the math, you will need to know how often optimal transfer windows open up (26 months for Earth, Mars). What is the best-case scenario for delta-vee expenditure (5,700 m/s) and the worst-case (let's call it 10 km/s). Then you can just roll to see how far away the next optimal transfer window is. If you are 6 months out for example, you can extrapolate to be 7.8 km/s). As for time, take half the orbital period of the target's orbit around the sun.

View attachment 6225

For something a bit more complex, let's consider the Gemini 6 mission to rendezvous with Gemini 7.

For this mission, NASA decided to do what they called a co-elliptic rendezvous in four orbits. The main reason is that they will have several opportunities to adjust the time of rendezvous for the optimal lighting conditions.

View attachment 6227
On the right, you can see the general scheme drawn as orbits around the Earth. On the left, you can see a plot of the range to the target and how far Gemini 6 will be below Gemini 7. Each peak you see is the apogee of Gemini 6's orbit as Gemini 7 is in a near circular orbit.

This what their maneuver plan looks like (also includes what happen on Gemini 8). Rev stands for Revolution (Orbit)
View attachment 6228
Here is the plot of Gemini with time marked as well as horizontal and vertical range from Gemini 7.

View attachment 6229
  • Gemini 6 launched and then passed its first apogee (the highest point of its orbit).
  • Then, at first perigee (lowest point), they executed a height adjust, which is the first step to get the timing for the rendezvous right.
  • Then, at the 2nd apogee, they execute a second burn that was the most crucial in setting up the timing for the rendezvous.
  • While not shown, on the way to the second perigee, they will arrive at a point where the orbital plane of Gemini 7 will intersect the orbital plane of Gemini 6. Gemini 6 will make a burn to align its orbital planes.
  • Finally, a final height adjustment is made at the second perigee to tweak the timing further. Remember, there are small factors like atmospheric drag and solar wind, which cause small adjustments to be needed at various points to keep the trajectory on track.
  • Finally, at the third apogee, Gemini 6 circularized its orbit about 15 nautical miles below Gemini to setup the terminal phase transfer at the TPI point.

Terminal Phase Transfer​

View attachment 6230

So as it turns it, it is pretty straight forward to do the terminal phase transfer. You need three things.
  • Range to Target (Radar)
  • Rate of Closing (Radar)
  • A Fixed Point in space (A Star)
Now, keep in mind Gemini 6 is in a lower orbit than Gemini 7, so they are travelling faster. The trick is that you wait until the target is a certain degree above the horizon using the stars as a reference (27 degrees in the case of Gemini 7). Your radar will show you closing in on the target. Now, if you don't do anything what will happen is your rate of closure will drop to zero as you pass the target in the lower orbit and then you will see yourself pulling away.

So what you do instead is start thrusting toward the target to maintain the right rate of closure while continuing to point your nose at the target. As you are below and behind the target, this will raise your orbit at first. Eventually, this will cause you to slow down faster relative to your target, but because you are always pointing at them, you will thrust to maintain the correct speed at the correct time. This effect is negated as you swing below and past the target. You will then curl around, still facing the target, and if you follow the plan correctly, you will be around 100 meters away at zero relative velocity (TPF)

For Gemini 6, Wally Schirra was helped by this, which was configured to make it easy for him to maintain the correct velocity at the correct range. The goal was to keep the white indicator in line with the striped indicator.

View attachment 6232

Note on Gemini 12 with Jim Lovell and Buzz Aldrin the radar failed on the way to their Agena Target Vehicle. Buzz Aldrin used a set of charts that he had made before the flight and a sextant to guide his commander to rendezvous with the Agena. The principle was the same except Buzz Aldrin was using optical tools like the sextant to get range and rate of closure.



Hope this is helpful. The point is to give a referee a sense of what goes into realistic space maneuvers, so they can understand which skills would come into play at different times.
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I missed a couple of weeks of the forum due to bs real life demands, but I log in and find this. Thank you! This was clear and substantially more concise than Buzz Aldrin’s book on Orbital Maneuvers. Looking forward even more to launch tomorrow.

Michael
 
Michael S said:
I missed a couple of weeks of the forum due to bs real life demands, but I log in and find this. Thank you! This was clear and substantially more concise than Buzz Aldrin’s book on Orbital Maneuvers. Looking forward even more to launch tomorrow.

Michael
Click to expand...
Thanks! I am very excited for Pioneer's launch as well.
 
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