What just happened?

[SilverAstro]

5 minutes ago, Luna-tic said:

Add to that the stronger magnetic field of Jupiter, can influence a travelling body much further out from its surface, and most meteoric masses travelling inside the solar system are being influenced by solar gravity (they are travelling roughly towards the Sun) and their velocity out at Jupiter's orbit is less than it would be at Earth's orbit due to the acceleration constant of the Solar gravity well.

Pete mentioned above that he'd like to "witness one live". So would I, as long as I was outside the blast radius.

Yes all the above, and a few other things*, are all encompassed in the deltaV

May I modify your "witness one live" ,,, witness one Alive ,,

* for example, capturing an asteroid into earth orbit for mining. An ion thruster or similar gives it dV to start it off heading this way, but it would fly right past us and back out unless another dV was applied near here.

1 minute ago, Stu said:

So, by extension of this, an Apollo mission heading to the moon would just slingshot around and head back towards earth without a retro burn to slow it down into orbit?

exatamont ! You got it

 

[SilverAstro]

12 minutes ago, Stu said:

 just slingshot around and head back towards earth without a retro burn

As (I think ? *) did the miracle that was Apollo 13, I think it was all recovered by minor thruster burns ?? not sure it is all a long time* ago , as indeed the last time I did orbital dynamics was just before then !

Just a small point, I'm not sure but I think the term 'retro' is used for de-orbiting (ie returning to surface etc) I have hazy memories of 'orbit insertion' burn for others ? Principle is the same though  ( but that is by way of stumbling back up the cliff   )

[wxsatuser]

52 minutes ago, Stu said:

So, by extension of this, an Apollo mission heading to the moon would just slingshot around and head back towards earth without a retro burn to slow it down into orbit?

Yes, it is possible to get out of jail with a free return.

Basically the TLI, Trans Lunar Injection is a Hohmann transfer orbit which is an eliptical orbit used to transfer between to circular orbits in the same plane.

 

[Luna-tic]

5 hours ago, SilverAstro said:

As (I think ? *) did the miracle that was Apollo 13, I think it was all recovered by minor thruster burns ?? not sure it is all a long time* ago , as indeed the last time I did orbital dynamics was just before then !

Just a small point, I'm not sure but I think the term 'retro' is used for de-orbiting (ie returning to surface etc) I have hazy memories of 'orbit insertion' burn for others ? Principle is the same though  ( but that is by way of stumbling back up the cliff   )

TLI is designed to establish a trajectory to the Moon that provides for a free return trajectory (with minor course corrections enroute) should the SPS [service propulsion system] engine fail to fire at LOI [lunar orbit insertion]. The LOI burn created a 3000 fps Delta-V to achieve lunar orbit from the free return trajectory. Since the SPS was not functional on Apollo 13 due to the O2  tank explosion, the throttle-able LEM descent engine was used for course corrections, both on the way out and the way back.

This is an interesting read; seems that we were at the very edge of technology of the day to land and take off again from the Moon:

https://history.nasa.gov/afj/loiessay.html

[SilverAstro]

1 hour ago, Luna-tic said:

 provides for a free return trajectory (with minor course corrections enroute)

seems that we were at the very edge of technology of the day to land and take off again from the Moon:

Thanks for that, I was mis-remembering thrusters* for the LEM decent engine (5 decades - I am just chuffed that I can remember some of it !   )

(* I slipped into a memory warp as I had a lot of payload aggro for my telecoms/telemetry [not Apollo, other spacecraft ! ]  vs. the mechanics wanting lots of Hydrazine thruster capacity for station keeping !   )

Absolutely at the limit and almost beyond. I am even now uncertain which was the greater achievement.  the A11 landing which went according to plan (just!), or the amazing ability to recover from the A13 disaster and bring them (edit,- themselves) home alive ? (still gives me shivers remembering the time sat on the edge of my, comfortable, seat )

 

[Revilo]

On 1/17/2018 at 01:38, brodon83 said:

Ok I'm here in Michigan and my house just shook! People in a 3 hour driving radius all reporting seeing bright flash in the sky. Anybody have any inside info. We're we expected to have a major hit!

Apparently they  are called bolides this sounds similar to what you just had https://en.m.wikipedia.org/wiki/Bolide

[SilverAstro]

PS. the Earth -> Apollo -> Moon orbits were a combination,  including a modified Hohmann transfer orbit , the prototype Hohmann transfer is a two body (we are back to bodies! ) solution to raise the orbit of a small secondary ( satellite/moon/rock) in the presence of a (large) primary by way of an intermediary ellipse.

It is more relevant to Mars missions where two larger bodies (and their gravity wells) are well separated (more than that of the Earth-Moon combo)

but I think that is a discuss for another place ?

On the other hand, if anyone wants to follow up this type of subject, one could investigate apogee boost motors, (orbit transfer),  their weight, and that of their propellent, and how it cut down into my need for power (RTG) to get the science data over the watts of the telemetry link once the spacecraft had got to where we wanted it to be !