ESA Rosetta: Burning down to 67P/C-G comet rendezvous

ESA Rosetta's target comet, 67P/Churyumov-Gerasimenko, is about 4 km wide. 

Here it is presented alongside some of Earth's landmarks. 

Image courtesy ESA.

It's burn week in space again, and Wednesday, 2 July, marks the start of a fresh set of four orbit correction manoeuvres (OCMs), referred to as the "Far Approach Trajectory" burns.

These will be somewhat smaller than those previous but will be conducted weekly, rather than fortnightly. First, a quick recap to bring you up to date.

On 7 May, Rosetta began a series of ten OCMs designed to reduce its speed with respect to comet 67P/C-G by about 775 m/s.

The first, producing just 20 m/s delta-v ("change in velocity"), was done as a small test burn, as it was the first use of the spacecraft's propulsion system after waking from hibernation on 20 January. The system worked fine!

The following three, referred to by the Rosetta mission team as the "Near Comet Drift" (NCD) set (and nicknamed here in the blog as "The Big Burns"), took place every two weeks starting 21 May.

These three also ran beautifully and delivered 289.6, 269.5 and 88.7 m/s in delta-v, respectively. They were, in terms of run time, some of the longest manoeuvres ever conducted by an ESA spacecraft.

Thus the first four burns have already delivered 667.8 of the roughly 775 m/s needed to slow down to a relative velocity smaller than 1 m/s when we meet the comet on 6 August.



"The OCMs conducted so far have delivered more or less the exact amount of delta-v needed; we've seen small over-performances of less than a percent, meaning that no replanning of subsequent OCMs has, so far, been necessary," says Sylvain Lodiot, Rosetta Spacecraft Operations Manager.

Another aspect of the burns to date is the fact that, if a burn did not take place as planned (due to any sort of glitch on board Rosetta or on the ground), the team had a week (or more) in which to correct the problem and re-do the burn, tight, but doable in terms of technology and team-planning workload.

This is about to change.

Four Fatties
The next four burns are designated as the "Far Approach Trajectory" (FAT) manoeuvres, and since your blog editors can't think of any better nickname (and despite them being much smaller than the three Big Burns), we'll just call them the "Four Fatties".

Fatty1 gets underway on 2 July at 14:05:57 CEST (12:05:57 UTC), should run for 1 hr:33mins:13secs and is set to deliver a delta-v of 58.7 m/s (the next three, on 9, 16 and 23 July, are planned for 25.8, 11.0 and 4.8 m/s, respectively).

(The Four Fatties will be followed by two final CAT for Close Approach Trajectory - burns, for the total of 10 OCMs; details on these later.)

But while the required delta-v's are getting smaller, so, too, are the reaction times available to the Rosetta team if anything goes wrong with a burn.

"The next four FAT burns, in particular, are critical," says Sylvain.

If any one burn is delayed, we will have a window of just a few days in which to react, fix whatever caused the problem, replan the burn - which would invariably require even more fuel - and then carry it out."

It goes without saying that handling any such replanned burn would require team work and expertise of the highest calibre.

But this is all theoretical for now; today Rosetta is working nominally and no one expects problems with the propulsion system for the Four Fatties.

The rest of the spacecraft's systems - including power, thermal, attitude and orbit control, data handling and communications, are operating as expected.

Read the full article here

CheetahCub: EPFL's Biorobotics Lab robot that runs like a cat - Video

Thanks to the design of its legs, which faithfully mimic feline morphology, EPFL's four-legged "cheetah-cub robot" shares the advantages of its biological model: it is small, light and runs very fast. 

In the long term, this type of machine, which is still in an experimental stage, could be used in search and rescue missions or for exploration.  Credit: EPFL

Thanks to its legs, whose design faithfully reproduces feline morphology, EPFL's 4-legged 'cheetah-cub robot' has the same advantages as its model: It is small, light and fast.

Even though it doesn't have a head, you can still tell what kind of animal it is: the robot is definitely modeled upon a cat.

Developed by EPFL's Biorobotics Laboratory (Biorob), the "cheetah-cub robot," a small-size quadruped prototype robot, is described in an article appearing today in the International Journal of Robotics Research.

The purpose of the platform is to encourage research in biomechanics; its particularity is the design of its legs, which make it very fast and stable.

Robots developed from this concept could eventually be used in search and rescue missions or for exploration.

This robot is the fastest in its category, namely in normalized speed for small quadruped robots under 30Kg.

During tests, it demonstrated its ability to run nearly seven times its body length in one second.

Although not as agile as a real cat, it still has excellent auto-stabilization characteristics when running at full speed or over a course that included disturbances such as small steps.

In addition, the robot is extremely light, compact, and robust and can be easily assembled from materials that are inexpensive and readily available.

Faithful reproduction
The machine's strengths all reside in the design of its legs. The researchers developed a new model with this robot, one that is based on the meticulous observation and faithful reproduction of the feline leg.

The number of segments – three on each leg – and their proportions are the same as they are on a cat. Springs are used to reproduce tendons, and actuators – small motors that convert energy into movement – are used to replace the muscles.

"This morphology gives the robot the mechanical properties from which cats benefit, that's to say a marked running ability and elasticity in the right spots, to ensure stability," explains Alexander Sprowitz, a Biorob scientist. "The robot is thus naturally more autonomous."