View Full Version : Ep. 84: Getting Around the Solar System

2008-Apr-15, 04:40 AM
Have you ever wondered what it takes to get a spacecraft off the Earth and into space. And how managers at NASA can actually navigate a spacecraft to another planet? And how does a gravity assist work? And how do they get them into orbit? And how do they land? So many questions…http://feeds.feedburner.com/~r/astronomycast/~4/270450980

More... (http://feeds.feedburner.com/~r/astronomycast/~3/270450980/)

2008-Apr-19, 05:34 AM
Hello Fraser and Pamela and Rebecca,

Love the podcast... your efforts have educated, entertained and enlightened me for many hours over the last few months... many many thanks.

In the 'getting around' podcast I think you might have missed mentioning a rather good subtopic.... rendezvous in orbit.

I may have it wrong, but I believe that if you took a random, middle-aged, thinks-he-is-a-great-driver... (me! me!..... take me!!).... and stuck him on a rocket broomstick in a orbit a few minutes behind the ISS and said ok mate.. drive over to the airlock... he would be in all sorts of trouble.

Unless I have my facts wrong, nearly everything he needs to do with his rocket is counter-intuitive... he needs to reverse orientation and fire a braking thrust to lower his orbit.... come up under and in front and then fire a accelerating thrust to lift and match orbits... and he needs to massively think ahead and act early for all his fine controls. Sounds like fun.

I can imagine the conversation Fraser and Pamela could have on this topic and I bet it would be worth listening to... As I say, I could have my facts wrong... but I thought it might be worth mentioning.

Best regards and thanks again,

2008-Apr-22, 10:52 PM
I have not studied celestial mechanics, but I believe I know enough about the basic priniciples to answer your question.

Suppose you and the ISS are in coplanar circular orbits around the earth and you want to dock with it. To minimize fuel consumption, you should need to do this via an elliptical transfer orbit with appropriate apigee (high) and perigee (low) points. To enter the transfer orbit, you would need to use your thruster briefly to increase your speed to that for the transfer orbit just as you reach the transfer orbit. The transfer orbit would need to cross the ISS's orbit just as the ISS was passing the crossing point, On reaching the ISS's orbit, you would need to use the thruster again to decrease your speed to match the speed of the ISS. Identifying the appropriate time and thrust for entering the transfer orbit and the approprirate thrust to use in leaving it would be laborious without use of a computer.

2009-Jan-16, 10:25 PM
I imagine one might use the moon's gravity to slow down during an approach to Earth...

2010-Feb-11, 07:05 PM
Oh, the horror! Lucky for me, I'm only on the Uranus episode, so I still have a few more to catch up on before I *need* #84. Doubly lucky for me, the guy that turned me on to Astronomycast has a copy of #84 and will get it to me.

Here's the story as I know it:

- Went to http://www.astronomycast.com/
- Clicked on 'Archive' (points to http://www.astronomycast.com/archive/)
- Scrolled down to #84 in the archive list (04/14/2008 84 Getting Around the Solar System)
- Clicked on 'Download' for #84 (points to http://media.libsyn.com/media/astronomycast/AstroCast-080414.mp3)
- Received 404 error

To try to find this episode another way, I next tried clicking on the title for #84 (points to http://www.astronomycast.com/astronomy/planetsour-solar-system/ep-84-getting-around-the-solar-system/). This brought me to the summary page for that episode, which also provided a link to download it. Unfortunately, this link points to the same place, and results in the same error.

Just to be thorough, I search the forum associated with Astronomy Cast, and could not find any other reports of this missing file.

Now, on the 404 page, it directs you to notify support@libsynpro.com, so I did on Feb 4, but have not heard back yet (nor is the episode available today). I gave them the summary provided above (actually, the above content is mostly a copy/paste from the mail I sent them).

2010-Feb-12, 02:29 AM
I'm having the same problem with Episode 167: Future Civilizations.