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Venus Express
RNeuhaus
post Oct 12 2005, 04:09 AM
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New update. Now it is less than 14 days from launching on October 26 from Baikonour Cosmodrome.

Venus Express ready for 'mating' with upper-stage

* Propellant loading already completed. Two tanks with more than 260 liters capacity.
* Venus already has its wings. Provides 1,100 watts of power. It is made of Gallium Arsenide Triple Junction
* Electrical test completed. Automatic sequence of maneuvers works.

Almost ready for a trip of 153 days toward to Venus for a mission of 500 days in Venus orbit.
Launch mass is 1,270 kg.

Rodolfo
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ljk4-1
post Oct 13 2005, 01:50 PM
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Preparations for ESA's Venus Express mission passed a new milestone when the
spacecraft was attached to its Fregat upper-stage rocket. The mission is now
only two weeks away from launch on 26 October.

More at:

http://www.esa.int/SPECIALS/Venus_Express/SEMTYW5Y3EE_0.html


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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RNeuhaus
post Oct 13 2005, 02:45 PM
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The spacecraft Technical details

Spacecraft facts
Spacecraft bus dimensions 1.5 x 1.8 x 1.4 m
Spacecraft mass 1270 kg (including 93 kg of payload and 570 kg fuel)
Thrust of main engine 400 N
Attitude thrusters Two sets of four, each delivering 10 Newtons each
Solar arrays Two triple-junction Ga As;
5.7 square metres; generating 800 Watts
near Earth and 1100 Watts at Venus
Power storage Three lithium-ion batteries
Antennas Two high-gain dishes, HGA1 = 1.3 m diameter,
HGA2 = 0.3 m in diameter, 2 low-gain antennas

Venus Express

The proportion of total weight versus fuel is 44.8% of weight is fuel comparing to the MRO (1,187 kg of fuel hydrazine of 2,180 kg = 54.4% to reduce 1.4 KM/sec during the orbit insertion.) I have not found how the Venus Express will insert into the Venus. At what speed and the what orbit will be traveling VE (Polar, some inclination Equatorial).

The panel solar is very small : 5.7 M^2 versus 10 M^2 of MRO. VE will have about 1,100 Watts and MRO around 1,000 Watts of power when these spacecraft are in their orbits. VE uses Lithium-ion batteries and MRO uses Nickel-hydrogen batteries. What is the difference?

Rodolfo
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um3k
post Oct 13 2005, 03:03 PM
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QUOTE (RNeuhaus @ Oct 13 2005, 10:45 AM)
The panel solar is very small : 5.7 M^2 versus 10 M^2 of MRO. VE will have about 1,100 Watts and MRO around 1,000 Watts of power when these spacecraft are in their orbits. VE uses Lithium-ion batteries and MRO uses Nickel-hydrogen batteries. What is the difference?

Rodolfo
*

I'm no expert, but I would venture to guess that the cause is the spacecrafts' distances from the sun.
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Rakhir
post Oct 13 2005, 04:03 PM
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QUOTE (RNeuhaus @ Oct 13 2005, 04:45 PM)
The spacecraft Technical details

I have not found how the Venus Express will insert into the Venus.

Rodolfo
*


From http://esamultimedia.esa.int/docs/VENUSEXPRESSLR.pdf

"In April 2006, it will fire its main engine to slow down and counteract the predominant pull of the Sun and of Venus, to be captured into orbit around the planet. A large velocity change is required for the initial capture manoeuvre, which will require the engine to burn for 53 minutes."

Orbit details -> see page 8 of the pdf cool.gif
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RNeuhaus
post Oct 13 2005, 04:46 PM
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QUOTE (Rakhir @ Oct 13 2005, 11:03 AM)
From http://esamultimedia.esa.int/docs/VENUSEXPRESSLR.pdf

"In April 2006, it will fire its main engine to slow down and counteract the predominant pull of the Sun and of Venus, to be captured into orbit around the planet. A large velocity change is required for the initial capture manoeuvre, which will require the engine to burn for 53 minutes."

Orbit details -> see page 8 of the pdf cool.gif
*

Thanks Rakhir, Regrettable, this link needs some kind of authorization.

Forbidden

Your request cannot be serviced due to access restrictions. Please contact your System Administrator for further details

ERROR: your request cannot be serviced

Rodolfo
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tedstryk
post Oct 13 2005, 05:06 PM
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QUOTE (RNeuhaus @ Oct 13 2005, 04:46 PM)
Thanks Rakhir, Regrettable, this link needs some kind of authorization.

Forbidden

Your request cannot be serviced due to access restrictions. Please contact your System Administrator for further details

ERROR: your request cannot be serviced

Rodolfo
*


Works just fine for me.


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ugordan
post Oct 13 2005, 05:09 PM
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QUOTE (RNeuhaus @ Oct 13 2005, 06:46 PM)
Thanks Rakhir, Regrettable, this link needs some kind of authorization.

Forbidden

Your request cannot be serviced due to access restrictions. Please contact your System Administrator for further details

ERROR: your request cannot be serviced

Rodolfo
*


I had no problems accessing the pdf just now. Did you try opening the link with a different browser or anything?
I don't know if uploading the document is allowed here due to copyright restrictions?


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RNeuhaus
post Oct 13 2005, 06:25 PM
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The problem was already solved by changing the proxy IP Address.

Thanks,

Rodolfo
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Jeff7
post Oct 14 2005, 04:22 AM
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QUOTE (um3k @ Oct 13 2005, 10:03 AM)
I'm no expert, but I would venture to guess that the cause is the spacecrafts' distances from the sun.
*

I think the part in question was the composition of the batteries - lithium ion vs nickel hydrogen.
I know about li-ion, but I don't know a lot about nickel-hydrogen. I think Hubble also uses the latter type.
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helvick
post Oct 14 2005, 08:15 AM
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QUOTE (Jeff7 @ Oct 14 2005, 05:22 AM)
I think the part in question was the composition of the batteries - lithium ion vs nickel hydrogen.
I know about li-ion, but I don't know a lot about nickel-hydrogen. I think Hubble also uses the latter type.
*


Li-Ion has better power density but the varous Nickel Hydrogen designs, like the NimH used on some laptops and other consumer electronics kit, has much better charge cycle lifetime. Li-Ion is generally good for up to 1000 charge cycles while there are Ni H designs that are spec'ed out for 30000. NimH batteries also have the benefit of being able to be re-conditioned however I don't know if the process is suitable for use "in flight" with the pressurised NiH type batteries used on spacecraft. Li-Ion degradation is more or less permanent.

There are many other considerations though so the cycling capability is only one possible reason.
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Rakhir
post Oct 14 2005, 08:23 AM
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QUOTE (um3k @ Oct 13 2005, 05:03 PM)
I'm no expert, but I would venture to guess that the cause is the spacecrafts' distances from the sun.
*


From the pdf of my previous post : "The sun is twice as strong at Venus as on Earth, so there is plentiful solar radiation to power the spacecraft. VE's solar arrays could therefore be made smaller (almost half the size) than those on Mars Express."
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RNeuhaus
post Oct 14 2005, 03:59 PM
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QUOTE (Jeff7 @ Oct 13 2005, 11:22 PM)
I think the part in question was the composition of the batteries - lithium ion vs nickel hydrogen.
I know about li-ion, but I don't know a lot about nickel-hydrogen. I think Hubble also uses the latter type.
*

I didn't mention well in my last post. You posted is what I was asking about this: What are the differences between the two different types of batteries?

Rodolfo
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RNeuhaus
post Oct 14 2005, 04:22 PM
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According to the VE's pdf document, VE has greater challenge to orbit around Venus than Mars Express since it has two great concern that must be adjusted continuously:

1) The thrusters has to adjust to correct the altitude of orbit's pericentre approximately once every day. In fact, due to the gravitational pull of the Sun while the spacecraft is further away from the planet, the pericentre naturally drifts upwards at a rate of about 1.5 kilometres per day.

2) For a spacecraft in orbit around Venus, it is not always possible to point a single
antenna dish at Earth while always keeping the cold face of the spacecraft, hosting
delicate instruments, away from the Sun.To overcome this pointing constraint,Venus
Express has two high-gain antennas mounted on different spacecraft faces.The
main high-gain antenna, used for most of the communications with Earth, is a 1.3
metre-diameter dish.The second, smaller high-gain antenna (30 centimetres
diameter) is used when the spacecraft is in the part of its orbit closest to Earth (less
than 0.78 AU* away).

On the other hand:

I have a doubt about the VE's trajectory to Venus. Will the Soyus-Fraget travel in the opposite way to the Earth's rotation before going to Venus?

I tought it since the Earth position is on the apehelion comparing to the Venus position as perihelion. Hence, the trajectory from Earth to Venus is of inward bound. To launch a spacecraft from Earth to an inner planet such as Venus using least propellant, its existing solar orbit (as it sits on the launch pad) must be adjusted so that it will take it to Venus. In other words, the spacecraft's aphelion is already the distance of Earth's orbit, and the perihelion will be on the orbit of Venus.

This time, the task is to decrease the periapsis (perihelion) of the spacecraft's present solar orbit. A spacecraft's periapsis altitude can be lowered by decreasing the spacecraft's energy at apoapsis. To achieve this, the spacecraft lifts off of the launch pad, rises above Earth's atmosphere, and uses its rocket to accelerate opposite the direction of Earth's revolution around the sun, thereby decreasing its orbital energy while here at apoapsis (aphelion) to the extent that its new orbit will have a perihelion equal to the distance of Venus's orbit. Of course the spacecraft will continue going in the same direction as Earth orbits the sun, but a little slower now. To get to Venus, rather than just to its orbit, again requires that the spacecraft be inserted into its interplanetary trajectory at the correct time so it will arrive at the Venusian orbit when Venus is there. Venus launch opportunities occur about every 19 months.



Will do VE follow the trajectory of least energy orbit as mentioned above?

Rodolfo
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dvandorn
post Oct 15 2005, 08:59 AM
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Your diagram shows the most common Hohmann transfer orbit, achieved by reducing the aphelion to coincide with the orbit of Venus (preferably when Venus itself is occupying that point along its own orbit).

There is another type of Hohmann trajectory for this type of mission. Instead of braking against the Earth's solar orbital velocity, the spacecraft thrusts at right angles to Earth's near-circular orbit (likely directly towards the Sun), creating a lopsided orbit with a perihelion at Venus and an aphelion well outside of Earth's orbit. The good thing is that the average orbital velocity of such an orbit is very nearly the same as the Earth's velocity, so you don't need to brake so much. The bad thing is that it takes even more energy to enter this transfer orbit, and your approach speed at Venus is somewhat higher, requiring more energy to brake you into orbit.

It gets you there a little faster than the brake-against-solar-orbit method, but it takes more energy.

-the other Doug


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“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
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