Comet landing tomorrow!

[hifly 925]

 

 

 

 

 

 

 

Batteries could teoretaclly recharge over next few days.

 

 

teoretically? A touch of the iorish there Martin?

 

Top o the milk!  

 

PS John & Mark. Bunfight def; A petty squabble.

 

[allardjd 1,853]

...what's a Hampden

 

 

From Wiki...

 

The Handley Page HP.52 Hampden was a British twin-engine medium bomber of the Royal Air Force serving in the Second World War. With the Whitley and Wellington, the Hampden bore the brunt of the early bombing war over Europe, taking part in the first night raid on Berlin and the first 1,000-plane raid on Cologne. The newest of the three medium bombers, the Hampden, known as the "Flying Suitcase" because of its cramped crew conditions,[1] was still unsuited to the modern air war and, after operating mainly at night, it was retired from Bomber Command service in late 1942.

 

It looks a little like the DO-17 from certain angles - twin rudders and a slim aft fuselage.

[MartinW 0]

 

Batteries could teoretaclly recharge over next few days.

 

teoretically? A touch of the iorish there Martin?

 

Top o the milk!

 

PS John & Mark. Bunfight def; A petty squabble.

 

 

 

Sorry about that, I guess I was on my phone again. Need reading glasses but can't be arsed to buy them. And my son works for an optician as well.

 

P.S. I am 1/8th Irish.

[MartinW 0]

...what's a Hampden

 

From Wiki...

 

The Handley Page HP.52 Hampden was a British twin-engine medium bomber of the Royal Air Force serving in the Second World War. With the Whitley and Wellington, the Hampden bore the brunt of the early bombing war over Europe, taking part in the first night raid on Berlin and the first 1,000-plane raid on Cologne. The newest of the three medium bombers, the Hampden, known as the "Flying Suitcase" because of its cramped crew conditions,[1] was still unsuited to the modern air war and, after operating mainly at night, it was retired from Bomber Command service in late 1942.

 

It looks a little like the DO-17 from certain angles - twin rudders and a slim aft fuselage.

 

 

Thanks John not heard of it before. Shows how limited my aircraft knowledge is. Interesting aircraft.

http://en.wikipedia.org/wiki/Handley_Page_Hampden

[markhudson6 13]

Really interesting link to the Hampden John, cheers.

 

The wiki notes that the Soviet's operated the aircraft.  Are their other examples of Western aircraft being operated by the Soviets during this time? 

 

Sad that Philae is now in standby.  Did ESA attempt to move it before it shut down?

 

 

[MartinW 0]

Don't think they did Mark, didn't see anything on the Twitter feed anyway. I also follow Emily Lakdawala from the Planetary Society, I didn't see anything from her either and her Philae tweets have been exceptional.

Engineers did send a command to reorientate the lander though.

They raised Philae by 4cm and turned its main housing by 35%. This should ensure the largest solar panel catches the most light.

Good chance she will fire up when the comet gets closer to the sun.

[ddavid 149]

Mark, the Russians built several hundred DC-3's under licence during and after WWII.

Philae reportedly raised itself and re-otientated its antenna before sending its last data and shutting down. The ESA hope to revive the lander in 2015, when it is nearer the Sun and has a better chance of using its PV panels. The data transferred is currently being analysed, so we await disclosure of water and organic compound results.

Cheers - Dai

[markhudson6 13]

Cheers guys for the info.  Keeping my fingers crossed for the mission.  Dai, I remember now seeing Chinese DC-3's too.  Not sure if they were under license of just knockoff copies though.

[allardjd 1,853]

The Soviets also did a rivet by rivet copy of a B-29 that was interned late in the war in Eastern Russia after over-flying Japan.  They christened it the Tu-4 and built almost 850 of them.  I guess they must have liked it.

 

Re the lander, if I'm interpreting yesterday's articles correctly they decided to go for broke on the remaining battery life and employ the drill in an attempt to get sub-surface samples before the lights went out.  Not sure (and they didn't seem to be either) whether there would be enough amp-hours left to operate the analysis ovens, which are probably fairly high-current heaters.  

 

The comet surface photos don't look much different from the Eros asteroid that was investigated and was the site of a soft-landing by a probe in 2001, however if there are volatile substances in the comet, those must filter up through the regolith to escape in the solar wind.  

 

Though a soft landing was made on Eros in 2001, the vehicle had fewer instruments than the current one and none were intended for surface contact work.  The soft landing was an afterthought, almost a lark at the end of the program, though it was successful and one instrument ended up only about 4" from the surface and gave some unexpectedly good data after the landing.  

 

There's quite a difference in volume and presumably in mass between Eros and this body.  Eros was about 35 X 11 X 11 km and this comet is described as being about 4 km overall.  Approach and landing physics would be similar but somewhat different - assuming similar density of the bodies, less than three orders of magnitude.  The propensity to bounce or the ability to be easily relocated by small forces would be much greater on this comet than on Eros.

 

Hopefully they were able to burn the samples, catch the spectrum data and at least store it for later transmission.

 

For those who are comparing this to hitting a small target at a great distance, it is certainly all of that, however we should remember that these things are not simply a ballistic "bullet".  The designers employed sensors to determine location in space, a flywheel system to rotate the vehicle in any axis and thrusters to make course corrections.  It's a bullet, but a steerable one.

 

John

[hifly 925]

Here's a map I made of the Solar System with Rosetta, Philae and  comet 67P.

 

                                                        *< Uranus                                                                                                                < Venus     

 

      < Sun                                                                                                                                      < Earth

                                                                               67P >     < Philae                                                    < Moon

                                                                    < Rosetta

 

                                                  < Mars                                                                                                                                                       < Voyager

 

 

 

 

[markhudson6 13]

  Nice one Geoff and it's to scale.

 

Never knew that about the Tu-4 John, thanks for the heads up.  I've got some reading up to do 

 

 

[hifly 925]

  Nice one Geoff and it's to scale.

 

Never knew that about the T-4 John, thanks for the heads up.  I've got some reading up to do 

 

Thanks Mark, although Voyagers 1&2 should really be on pages 87 and 173 respectively.

 

Another piece of aviation history is that in the 1950s Rolls Royce sold Avon jet engines to the USSR.  I think the Americans were a bit pissed about that. 

[MartinW 0]

For those who are comparing this to hitting a small target at a great distance, it is certainly all of that, however we should remember that these things are not simply a ballistic "bullet".  The designers employed sensors to determine location in space, a flywheel system to rotate the vehicle in any axis and thrusters to make course corrections.  It's a bullet, but a steerable one.

 

John

The thruster was simply an attempt to counter the tendency to bounce on landing. Which failed of course. Part of the active decent system. Not sure if there are other thrusters for guidance, I believe not. Think it's just free-fall. Cold thrust system can be used for velocity adjustment I believe, but not steering.

The flywheel is designed to keep the lander upright in flight. Spinning it up to rotate it a little was an idea considered in an attempt to twist it toward the sun, but not the function it was designed for.

[allardjd 1,853]

Another piece of aviation history is that in the 1950s Rolls Royce sold Avon jet engines to the USSR.   I think the Americans were a bit pissed about that. 

 

 

It was the R-R Nene, not Avon, but it became the prototype for the engine that powered the Mig-15 Fagot, so yeah, I guess the US was probably not too happy about that.  

 

 

[allardjd 1,853]

No, the thruster was simply an attempt to counter the tendency to bounce on landing. Which failed of course. Part of the active decent system. Not sure if there are other thrusters for guidance, I believe not.

 

From Wiki:  "Main propulsion consists of 24 bipropellant 10 N thrusters.... Four of the thrusters are used for delta-v burns."

 

I believe those thrusters are used to adjust the velocity of the craft to refine the gravity assist maneuvers around other bodies, i.e. Earth (three times) and Mars for this particular craft.  

 

You cannot take a ballistic shot at something that far away and have any hope of ending up where you need to be.  It requires having some source of energy to adjust the trajectory as needed.  In this case, the thrusters adjust the velocity prior to a close-approach gravity assist "slingshot" maneuver around another body.  Each of those close approaches is essentially an opportunity for a course correction.

[mutley 4,498]

Here's a map I made of the Solar System with Rosetta, Philae and  comet 67P.

 

                                                        *< Uranus                                                                                                                < Venus     

 

      < Sun                                                                                                                                      < Earth

                                                                               67P >     < Philae                                                    < Moon

                                                                    < Rosetta

 

                                                  < Mars                                                                                                                                                       < Voyager

 

Geoff, your reply could well win my post of the year! If there was one 

[MartinW 0]

From Wiki: "Main propulsion consists of 24 bipropellant 10 N thrusters.... Four of the thrusters are used for delta-v burns."

I believe those thrusters are used to adjust the velocity of the craft to refine the gravity assist maneuvers around other bodies, i.e. Earth (three times) and Mars for this particular craft.

 

Yes, to adjust velocity, but Philae's thrusters aren't for steering. Not a "steerable bullet.

24 bipropellant 10 N thrusters are on Rosseta, not on the lander.

 

You were talking about the lander weren't you, when you said...

 

For those who are comparing this to hitting a small target at a great distance, it is certainly all of that, however we should remember that these things are not simply a ballistic "bullet". The designers employed sensors to determine location in space, a flywheel system to rotate the vehicle in any axis and thrusters to make course corrections. It's a bullet, but a steerable one.

 

 

[allardjd 1,853]

Yes, to adjust velocity, but Philae's thrusters aren't for steering. Not a "steerable bullet. 

 

 

 

No, Martin, that's incorrect.  Adjusting velocity is the only way you CAN steer it.  It's steered by controlling the velocity (and thus the height too) around a massive body during a close approach to it.  That IS the steering because changing that velocity changes the energy that's imparted to the probe by the nearby planet's gravity and changes the tangent at which the probe exits the gravitational assist maneuver.  

 

By the way, though Philae probably does have it's own thruster(s) for the landing maneuver, the delta-v thrusters are on Rosetta.  Philae is just a passenger for most of the trip.

[MartinW 0]

No, Martin, that's incorrect. Adjusting velocity is the only way you CAN steer it. It's steered by controlling the velocity (and thus the height too) around a massive body during a close approach to it. That IS the steering because changing that velocity changes the energy that's imparted to the probe by the nearby planet's gravity and changes the tangent at which the probe exits the gravitational assist maneuver.

John, we are talking about the lander here, yes? There is no gravity assist manoeuvre in regard to the lander. Rosetta yes, of course, I'm obviously aware of how Rosetta got there. How else could it get there.

The discussion is about the lander. Hence why you referred to Philae's flywheel. And hitting the target. The entire thread is about the lander.

[allardjd 1,853]

I mentioned this because of the posts about throwing a hammer from Britain and hitting a nail in Dubai, and no, I'm talking about Rosetta and it's passenger, Philae.  

 

Rosetta has thrusters that are used to make mid-course corrections as it makes a series of low passes around other massive bodies.  It's that process that got Rosetta/Philae in the neighborhood of the comet.  You can't simply fire a rocket from Earth ballistically and have it end up where you want it at those distances.  Mid-course "steering" is necessary and it's accomplished by modifying the velocity of the vehicle prior to each of the gravity assist passes.

 

[MartinW 0]

Yes John this is me you are talking to. You know that I know how Rosseta travelled to the comet. I' m the last person you need to explain the concept to.

But when you mention the flywheel in the same sentence, and we'd primarily discussed the lander, I will assume you are talking about the lander. Rosetta also has a flywheel reaction control system so thats where the confusion has come from.

[allardjd 1,853]

You know that I know how Rosseta works. I' m the last person you need to explain the concept to.

But when you mention the flywheel in the same sentence I will assume you are talking about the lander. If Rosetta also has a flywheel then thats where the confusion has come from.

Well, after that I hesitate to explain to you how Rosetta works, but yes, it has flywheels, or reaction wheels.  See below.

http://spaceflightnow.com/rosetta/140129update/#.VGfW5PnF-QU

"Engineers continued their methodical checkout of Rosetta over the weekend, spinning up three of the craft's four reaction wheels and transitioning responsibility for pointing and attitude control to the wheels from the probe's rocket thrusters, Accomazzo told Spaceflight Now.

Accomazzo said one of the three wheels now controlling Rosetta's orientation continued to show "non-nominal behavior" first observed before Rosetta entered hibernation in June 2011.

The other problematic reaction wheel will be held in reserve. Rosetta was designed to operate on three reaction wheels, but engineers devised new software to employ two wheels to keep the spacecraft pointed properly, ensuring its solar panels remain aimed at the sun, the antenna turned toward Earth and its science instruments trained on the comet once the probe arrives."

[MartinW 0]

I know, post above was edited to reflect that.

A simple misunderstanding.

[allardjd 1,853]

OK - fair enough.  Now, back to my original thought - yes, it's a long, long way to the comet, even further than to Tipperary, but the Rosetta/Philae vehicle isn't simply a bullet.  Intelligent hands gave it instructions for mid-course corrections as it went along, assuring that it ended up in roughly the same place at the same time as the comet and heading in the same general direction at approximately the same velocity.  That put it in position so Philae could proceed independently and do its own thing from a suitably short range.  

 

It's all a magnificent feat and a triumph of engineering but the analogy of the hammer thrown to Dubai isn't quite a parallel situation, since the Rosetta/Philae duo was steerable enroute.

[MartinW 0]

It's all a magnificent feat and a triumph of engineering but the analogy of the hammer thrown to Dubai isn't quite a parallel situation, since the Rosetta/Philae duo was steerable enroute.

 

 

Yes, I agree. However, we may be taking the "hammer thrown to Dubai" analogy a bit too seriously. If I recall, it was Delhi rather than Dubai, and I'm not exactly sure who made the analogy. It was probably an off-the-cuff comment made by one of the team, or maybe someone not even on the team. That's the problem with todays media, somebody makes a comment, and it doesn't matter if it's somewhat inaccurate, or if it's regretted the moment it's uttered, in a flash it's all over the internet for a multitude of individuals to analyse. But yes, you are correct, it isn't a good analogy, very few analogies are.

 

It's all a magnificent feat and a triumph of engineering

 

 

Yep, certainly is. 6.4 billion kilometres travelled, 10 years, twice the travel time to Eros, double the amount of time a mechanical failure could occur, endured the rigours of outer space for a decade, rendezvous and land on a comet travelling 135,000 kph.

 

The comet surface photos don't look much different from the Eros asteroid that was investigated and was the site of a soft-landing by a probe in 2001, however if there are volatile substances in the comet, those must filter up through the regolith to escape in the solar wind.

 

 

 

 

Wait till the comet gets closer to the sun. It's ices will start to sublimate, pebbles, dust and all manner of stuff will be released as giant geysers. It will look a whole lot different to Eros then.