Rosetta Ready To Land On A Larger Comet

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Rosetta Ready To Land On A Larger Comet
European Space Agency
October 28, 2003

With the launch of ESA's comet
chaser scheduled for February 2004,
the Rosetta team has been racing to
meet a new challenge - a change of
target.

Developed and planned over many
years, the pioneering Rosetta mission is one of the most challenging ever
undertaken in the history of space exploration. In May 2003, however, engineers
were presented with a new challenge when ESA's Science Programme
Committee announced that comet 67P/Churyumov-Gerasimenko would replace
comet 46P/Wirtanen as Rosetta's objective.

Not only were the two comets following different orbits and timetables, but the
team from ESA, industry and academia would have to prepare the Rosetta lander
for a hazardous descent onto a much larger ice world than originally anticipated.

Rising to the challenge, the team began to study the implications of exploring
Churyumov-Gerasimenko and the modifications that might be required to the
fragile lander. After months of intensive studies and simulations, engineers are
now confident that everything possible has been done to ensure that the
spacecraft will successfully complete history's first soft touchdown on a cosmic
iceberg.

"Comet Churyumov-Gerasimenko is a much bigger comet than Wirtanen," said
Philippe Kletzkine, ESA manager for the Rosetta lander. "It is about four times
the diameter and its gravity could be at least 30 times greater. This means that
the landing speed will increase from 0.2 - 0.5 metres per second to 0.7 - 1.5
metres per second.

"In the case of Wirtanen, our biggest problem was avoiding a rebound - the
spacecraft only had to bounce slightly and the momentum would overcome the
weak gravitational hold of the comet.

"Now, we also have to worry about absorbing the shock from a faster landing and
the stability of the lander upon touchdown. In the worst case scenario of a 'hard'
comet surface, rough terrain and relatively high gravity, it was possible that the
lander could topple over. In order to prevent this we decided to modify the landing
gear."

The design team wanted to avoid removing the landing gear or the entire lander
from the Rosetta orbiter, which is currently at the launch centre in Kourou, French
Guiana. They also wanted something, small, light and easy to fit. The answer was
a small bracket, known as a tilt limiter, that could be attached to the bottom of the
lander.

"By restricting the angle at which the landing gear can flex on touchdown to only 3
- 5 degrees, we improve the damping effect on touchdown and reduce the
possibility of a rebound," explained Jean-Christophe Salvignol, Rosetta lander
mechanical engineer.

"The limiter was designed by Astrium GmbH in collaboration with ourselves and
the Max-Planck-Institute in Lindau. During pendulum tests with a model of the
landing gear, we simulated landing on a wall at different angles of approach, and
verified that the spacecraft could successfully touch down at speeds of up to 1.5
metres per second on a 10 degree slope, or up to 1.2 metres per second on a 30
degree slope.

"In parallel, computerised simulations of landings were run by the
Max-Planck-Institute to better determine the landing performances for various
surface characteristics, impact velocities and lander attitudes."

The tilt limiter was finally delivered to Kourou and mounted on the spacecraft
landing gear on 30 September.

"This excellent collaboration between ESA, industry and MPAe has enabled us to
adapt to the new mission very quickly and efficiently," said Salvignol.

No major changes are envisaged for the lander's descent profile. However, under
the new mission scenario, there will be more time available for the orbiter's
instruments to map the nucleus in detail and find a safe haven for the 100 kg
lander.

The historic touchdown on the pristine surface of comet Churyumov-Gerasimenko
is expected to take place in November 2014. "We anticipate a landing on the
'summer' side of the nucleus, where there is maximum illumination," said Philippe
Kletzkine.

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Rosetta Launch Campaign Gets Underway
European Space Agency
November 4, 2003

The 2nd Rosetta Launch Campaign started formally on 24 October 2003. The
status today, 3 November, is that the Alenia AIV team has succesfully mounted
the High Gain Antenna (HGA) on the spacecraft and we are ready for the HGA
deployment test.

In parallel the Dutch Space solar panel experts are doing everything to ensure that the
Rosetta Solar Array's are ready to fly. Both solar arrays are still currently dismounted
and they are being inspected on the solar array rig. Once this is finished the arrays are
mounted on the spacecraft for the final deployment test.

In message , Ron Baalke
writes

http://sci.esa.int/science-e/www/obj...objectid=34098

Rosetta Ready To Land On A Larger Comet
European Space Agency
October 28, 2003


"Comet Churyumov-Gerasimenko is a much bigger comet than Wirtanen," said
Philippe Kletzkine, ESA manager for the Rosetta lander. "It is about four times
the diameter and its gravity could be at least 30 times greater. This
means that
the landing speed will increase from 0.2 - 0.5 metres per second to 0.7 - 1.5
metres per second.

How does that work out? I can see that the mass is about 64 times that
of Wirtanen, but doesn't landing speed scale up with the gravity?
--
Rabbit arithmetic - 1 plus 1 equals 10
Remove spam and invalid from address to reply.

In message , Ron Baalke
writes

http://sci.esa.int/science-e/www/obj...objectid=34098

Rosetta Ready To Land On A Larger Comet
European Space Agency
October 28, 2003


"Comet Churyumov-Gerasimenko is a much bigger comet than Wirtanen," said
Philippe Kletzkine, ESA manager for the Rosetta lander. "It is about four times
the diameter and its gravity could be at least 30 times greater. This
means that
the landing speed will increase from 0.2 - 0.5 metres per second to 0.7 - 1.5
metres per second.

How does that work out? I can see that the mass is about 64 times that
of Wirtanen, but doesn't landing speed scale up with the gravity?
--
Rabbit arithmetic - 1 plus 1 equals 10
Remove spam and invalid from address to reply.