Go Back  PPRuNe Forums > PPRuNe Social > Jet Blast
Reload this Page >

Cassini Grand Finale

Jet Blast Topics that don't fit the other forums. Rules of Engagement apply.

Cassini Grand Finale

Old 14th Sep 2017, 22:14
  #1 (permalink)  
Thread Starter
 
Join Date: Oct 1999
Location: Swindon, Wilts,UK
Posts: 563
Cassini Grand Finale

After one of the most successful missions and all that hard work poor Cassini is going out in a blaze of glory. I can understand the reasons why it's being done but it still seems a bit ungrateful.

To celebrate the end of the mission NASA have released a free e-book with some the highlights of the mission, its well worth a look at.
As the Russians would say, at least he's going out with music!
Windy Militant is offline  
Old 14th Sep 2017, 23:53
  #2 (permalink)  
 
Join Date: Apr 2000
Location: South of YSSY
Age: 68
Posts: 437
May as well leave it there, we can't bring it back and we seem to be happy to pollute other planets just as we are with our own. Just hope we get some more useful data from it before it melts on the way in.

Wonder how far into the atmosphere it will get before we lose contact?
criticalmass is offline  
Old 14th Sep 2017, 23:59
  #3 (permalink)  
Resident insomniac
 
Join Date: Aug 2005
Location: N54 58 34 W02 01 21
Age: 75
Posts: 1,859
When you (that is me) consider the complexity of the flight over the 29 years from conception with the various hitches and corrections and still the project ran its course, the people who conceived it and fixed the parameters must be very clever forward thinkers.

I'm particularly thinking about the slingshots around the various planets, but there is much much more.

Our Saturn years (scroll down for the whole story).




.

Last edited by G-CPTN; 15th Sep 2017 at 00:11.
G-CPTN is offline  
Old 15th Sep 2017, 09:42
  #4 (permalink)  
 
Join Date: May 2017
Location: Wrexham
Posts: 54
Let's hope there's nothing down there which dropping a hot core of plutonium onto won't affect/destroy/anger.
Animal Mother is offline  
Old 15th Sep 2017, 12:05
  #5 (permalink)  
 
Join Date: Sep 2002
Location: Great South East, tired and retired
Posts: 2,451
The Saturn version of Young Fat Wun will see this as an attack by the US and will launch his own inter-planetry terror and destruction the likes of which have never been seen before, blah blah blah.
Ascend Charlie is offline  
Old 15th Sep 2017, 18:17
  #6 (permalink)  
 
Join Date: Aug 2009
Location: Texas
Age: 60
Posts: 5,361
The residents of Saturn are probably not going to appreciate the suicide bombing of their planet. Luckily, it's small payload. Unluckily, now they're pissed.


All joking aside, good job the Cassini team for the mission and learning. Have a pint, you all earned it.
Lonewolf_50 is offline  
Old 15th Sep 2017, 19:15
  #7 (permalink)  
Ecce Homo! Loquitur...
 
Join Date: Jul 2000
Location: Peripatetic
Posts: 10,054
You know, since it is possible to slingshot your way around the solar system with zero fuel, it would be nice if they could bring one home. By which I mean unto earth or lunar orbit, even if it took 30 years. At some time it could be Collected and put in a museum.

One hell of an exhibit with the number of years, miles and exploits under its belt - and the inevitable pitting and damaged endured.

Requiem - Robert Louis Stevenson

Under the wide and starry sky
Dig the grave and let me lie:
Glad did I live and gladly die,
And I laid me down with a will.

This be the verse you 'grave for me:
Here he lies where he long'd to be;
Home is the sailor, home from the sea,
And the hunter home from the hill.
ORAC is online now  
Old 15th Sep 2017, 20:23
  #8 (permalink)  
Resident insomniac
 
Join Date: Aug 2005
Location: N54 58 34 W02 01 21
Age: 75
Posts: 1,859
Originally Posted by ORAC View Post
You know, since it is possible to slingshot your way around the solar system with zero fuel, it would be nice if they could bring one home. By which I mean unto earth or lunar orbit, even if it took 30 years. At some time it could be Collected and put in a museum.

One hell of an exhibit with the number of years, miles and exploits under its belt - and the inevitable pitting and damaged endured.
How would they land it?
G-CPTN is offline  
Old 16th Sep 2017, 04:48
  #9 (permalink)  
 
Join Date: Sep 2002
Location: Great South East, tired and retired
Posts: 2,451
It might accidentally land a little north of Seoul?
Ascend Charlie is offline  
Old 16th Sep 2017, 04:58
  #10 (permalink)  
 
Join Date: Apr 2001
Location: surfing, watching for sharks
Posts: 3,495
That's a lot of money spent for a museum piece.
West Coast is offline  
Old 16th Sep 2017, 06:56
  #11 (permalink)  
Ecce Homo! Loquitur...
 
Join Date: Jul 2000
Location: Peripatetic
Posts: 10,054
Look at it as being environmentally friendly......
ORAC is online now  
Old 16th Sep 2017, 08:03
  #12 (permalink)  
 
Join Date: Feb 2001
Location: The Winchester
Posts: 5,390
You know, since it is possible to slingshot your way around the solar system with zero fuel, it would be nice if they could bring one home.
"Gravity assist" is a heck of a technique but it has limitations.....You need something (planet, moon) in the right place, moving in the right direction to slingshot off in the required trajectory and unless you've planned ahead very carefully that probably means you need to do some manoeuvring (i.e. use fuel ) to get the spacecraft in the right trajectory to benefit from the slingshot.

If you look at the "flight paths" used by the likes of the Voyagers and Cassini the missions were planned from the get go with slingshot trajectories in mind and a lot of rocket fuel was expended in the first few minutes of the mission getting onto the initial trajectory that facilitated th subsequent slingshots..It would be pretty much impossible to perform a major change of plan and carry out a large "ad hoc" slingshot in the middle or end of a mission.
wiggy is online now  
Old 16th Sep 2017, 08:43
  #13 (permalink)  
Ecce Homo! Loquitur...
 
Join Date: Jul 2000
Location: Peripatetic
Posts: 10,054
I should have said minor rather than none, but as you point out, the hard work was done at the start of the mission.

My comment was based on a memory of the engineer who saved a mispositioned geostationary sattelite by slingshotting it past the Lagrange points and around the moon before it slid back into its planned geostationary slot. NASA then developed his work to be able to plot effective energy free "highways" amongst the planets.


CNN.com - New planet freeway could transform space travel - July 22, 2002

Last edited by ORAC; 16th Sep 2017 at 10:40. Reason: Sp
ORAC is online now  
Old 16th Sep 2017, 08:49
  #14 (permalink)  
 
Join Date: Feb 2001
Location: The Winchester
Posts: 5,390
Interesting stuff isn't it,(?.) Out of academic interest I wonder if there was ever any point in the Cassini mission where it would have been possible to at least "slingshot" it back in the general direction of Earth?

Thanks for the link...
wiggy is online now  
Old 16th Sep 2017, 10:25
  #15 (permalink)  
 
Join Date: Nov 2015
Location: Here
Posts: 295
Just out of interest , and of course its not the same type of spacecraft, but didn't they have to re-arrange the flight path/trajectory of the Apollo 13 mission midway to 'sling shot' it around the moon to get it back to Earth?
yellowtriumph is online now  
Old 16th Sep 2017, 10:46
  #16 (permalink)  
Ecce Homo! Loquitur...
 
Join Date: Jul 2000
Location: Peripatetic
Posts: 10,054
They did just about the same thing back in 1999 with Stardust, though they had it drop a canister off going past rather going into orbit or burning up in the atmosphere.
ORAC is online now  
Old 16th Sep 2017, 10:50
  #17 (permalink)  
 
Join Date: Feb 2001
Location: The Winchester
Posts: 5,390
didn't they have to re-arrange the flight path/trajectory of the Apollo 13 mission midway to 'sling shot' it around the moon to get it back to Earth?
Yes...well actually they had de-arranged it and had to quickly rearrange it

As I understand it on '13 and certainly on all the early Apollo flights ( in fact possibly all the Apollo flight) they intially left earth orbit using the final stage of the Saturn V on a trajectory that would loop around the Moon and return to earth if needed without any further intervention (hence it was called a "Free return Trajectory").

However "None free return" trajectories were needed to get access to the later Apollo landing sites ( a free return trajectory limits the choice of landing sites on the Moon, especially from a latitude POV, so from (I think) 13 onwards deviating from the free return became the norm..there's a whole load of fancy maths/papers in the NASA archives about exactly why that is so). To achieve this fairly soon after they were on their way and separated from the Saturn V the crews performed a short service Module engine "burn" to take them off this "free return trajectory"...doing it that way rather than going "direct" with the Saturn V gave them a supposedly fail-safe check of the Service Module engine, since if the engine didn't work they were stuck on a Free return, rather than on a "none free return"..


After the explosion on 13 one of the first things done was a short "burn" of the LM descent engine to put themselves back onto the Free return trajectory...I think Jim Lovell said something along the lines of them not wanting to end up as some permanently orbiting monument to the space program.

Right, where's that anorak.

Last edited by wiggy; 16th Sep 2017 at 11:07.
wiggy is online now  
Old 16th Sep 2017, 10:57
  #18 (permalink)  
Thread Starter
 
Join Date: Oct 1999
Location: Swindon, Wilts,UK
Posts: 563
Originally Posted by yellowtriumph
Just out of interest , and of course its not the same type of spacecraft, but didn't they have to re-arrange the flight path/trajectory of the Apollo 13 mission midway to 'sling shot' it around the moon to get it back to Earth?
I believe that all the Apollo missions were launched on a free return orbit. That is they were aimed go around the moon and slingshot back. Once it was established that they were go for lunar orbit they would hit the brakes, that is fire the Command Module engine and slow down enough to be captured by lunar gravity.

Apollo 13 fired the Lunar Lander engine to speed up the return to make sure they got back before the power and Oxygen ran out.
Windy Militant is offline  
Old 16th Sep 2017, 11:02
  #19 (permalink)  
Ecce Homo! Loquitur...
 
Join Date: Jul 2000
Location: Peripatetic
Posts: 10,054
Wiggy, as to your question at #14, I very much doubt it.

Cassini had to do a long burn to slow to Saturn orbital velocity on arrival. I think would have needed a long series of planned slingshots around Titan et al to get back enough speed to get back up to escape velocity in the right direction.
ORAC is online now  
Old 16th Sep 2017, 11:02
  #20 (permalink)  
 
Join Date: Oct 2002
Location: West Wiltshire, UK
Age: 67
Posts: 369
I'm amazed at several things about these older space probes, from their success, through their longevity to the amazing ability of the teams that designed and operated them for decades, especially the latter, when they had to come up with workarounds for problems quickly, often improvising some very creative solutions.

The very clever way they got around the design implementation cock up that meant there would have been a major Doppler frequency shift problem encountered when Huygens was released, by delaying the release of Huygens and moving Cassini's trajectory out to reduce the Doppler shift, so the relayed signal stayed within the receiver front end bandwidth and the decoder's pulse width frame acceptance window was a really clever bit of lateral thinking: The Space Review: How Huygens avoided disaster

The only thing that slightly worries me is that we may be losing the ability to design and build kit that works reliably for decades. These long-lived, beautifully engineered, bits of kit are in sharp contrast to a lot of modern technology that seems designed to only last a year or two.
VP959 is online now  

Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.