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I鈥檝e come to the Kennedy Space Center to witness the final launch of shuttle Endeavour.

George Nelson (bottom-right) attempts to control Solar Max using the MMU

It is due to lift off on Friday. The mission will see the delivery of the $2bn Alpha Magnetic Spectrometer to the International Space Station.

It is a strange time to be here. Shuttle retirement has naturally prompted a lot of discussion about the state of the US human spaceflight programme.

Many people have been recalling their most memorable shuttle moments.

For me, some of the most startling images were those of astronauts using the .

The backpack seemed to embody what the shuttle was all about and the things it enabled astronauts to do 鈥� to work in space.

I recall attempts in 1984 to retrieve the malfunctioning using the MMU.

Floating untethered from the shuttle, he hung on to Solar Max鈥檚 solar wings at one point in an effort to bring the rogue platform under control. It didn鈥檛 quite work but that wasn鈥檛 a problem related to the MMU.

The satellite was eventually grabbed by the shuttle arm and its electronics payload repaired. Twenty-seven years on and Nasa is still interested in satellite servicing as a concept. I鈥檝e been hearing here details of the final shuttle mission 鈥� 鈥� which will be taking up a test rig that will allow the to practise techniques for re-fuelling satellites.

The rig holds a series of tools Dextre can pick up to show how the fuel caps on spacecraft could be released in orbit to allow propellant tanks to be topped up. You can see a promotional video .

Dextre and the station鈥檚 robotic arm are the products of Canadian ingenuity and, in particular, of .

The company itself is already pushing ahead with a commercial proposition of its own known as the . This is likely to launch in 2015. It鈥檚 basically a robotic tanker.

It will go into near geosynchronous orbit some 36,000km above the planet, where it will service commercial and government satellites in need of additional fuel. Ultimately, MDA hopes SIS vehicles could also find work in moving satellites to new locations, or in carrying out simple maintenance tasks.

The latter might include releasing the antennas on satellites that had become stuck during deployment. Some satellites carry huge antennas that must be packed for launch and they don鈥檛 always unfurl correctly when commanded.

But it is re-fuelling that is the primary motivation behind the first mission.

Thierry Guillemin, the chief technical officer of satellite operator听, told me that shortage of propellant to keep its telecommunications satellites in position is the main reason the company has 听to retire the platforms:

鈥漈hat鈥檚 what it is for the majority of them; it鈥檚 why re-fuelling is attractive. We actually keep decommissioning perfectly healthy satellites just because they run out of the fuel needed to keep them at their orbital location. To give you an example: in the next couple of years, we will decommission several Intelsat 6 Series spacecraft - satellites that were launched at the end of the 80s, beginning of the 90s. These satellites have more than 20 years in orbit and they are perfectly healthy from the standpoint of both their housekeeping function and their communications payload 鈥� but they are running out of fuel.鈥�

Intelsat has agreed to purchase about 1,000kg of the fuel in SIS 鈥� about half its total load. It is likely government agencies will take up the other half.

You鈥檒l recall that it was Intelsat last year that temporarily lost control of its Galaxy 15 spacecraft. Dubbed 鈥淶ombie-sat鈥� by the media as it drifted past other satellites in orbit, it later became 鈥淧hoenix-sat鈥� as engineers managed to regain full command of the wayward platform. But the incident illustrated very well how in-orbit servicing could be a very profitable venture in the future. Thierry Guillemin again:

鈥滶ven though we did a pretty good job with Galaxy 15 in avoiding any interference with the 15 or so satellites that we had to fly by, it鈥檚 true that the geostationary orbit becomes more and more crowded and the removal or towing of objects is yet another area where the servicer might be used. This one has its own challenges of course because depending on the size of the debris and how it is tumbling in space, it may be more or less difficult to grab it and tow it. But once we start using this service in orbit, designs and technology will evolve and we will learn how to deal with anything.鈥�

Nasa and MDA/Intelsat are not the only ones pursuing the concept of in-orbit servicing. The German Space Agency (DLR), for example, has an idea it is developing called DEOS.

The German DEOS demonstration would show how to capture spinning satellites

This is a demonstration mission that will also fly around 2015. It comprises a couple of satellites. One will act as the 鈥渟ervicer鈥� and the other as the 鈥渃lient鈥� spacecraft in need of capture and 鈥渞epair鈥�.

The purpose of the mission is really to understand how best to approach other objects and practise strategies for grabbing them. This is no trivial matter, Professor Felix Huber, the director of DLR space operations and astronaut training, told me:

鈥滻n the longer term, our goal is to be able to capture any satellite with a robotic arm. This might be a satellite that has lost control; it might be spinning or whatever. Usually, if you have a geostationary satellite, you have the apogee engine where you can grab into the nozzle. This is relatively easy. Whereas with DEOS, what we want to demonstrate is that we can grab a satellite anywhere with the robotic hand, even if it is rotating.

"But when you make the grab, what you have to do is un-stiffen the robotic arm - just like when you catch a ball, you kind of decelerate it slowly. Otherwise, if you have a hard touch, it will simply bounce off. Capturing a satellite means that once you have grabbed it, you need somehow to weaken your arm to slow it down gently. You will probably have to rotate the servicer to get rid of the spinning moment, and then you are safe. This will be the future if you have a broken satellite.鈥�

With the space above our heads getting ever more crowded, the long-talked-about proposition of in-orbit servicing has to become a reality sooner or later. And not just servicing, but removing redundant satellites from the sky altogether.

It has been calculated that just removing a few key broken satellites would substantially reduce the potential for collision and a near-exponential growth in space debris over coming decades.

The robotic systems on the space station are key Canadian contributions to the ISS project

It sits, fists clenched and arms folded to the chest. is ready for action on the space station.

Humans have an innate need to explore. It cannot simply be left to robots

The first humanoid robot to go into orbit was carried up to the outpost in February on shuttle Discovery.

I wrote about this machine just prior to launch. It's now been , but won't be switched on for another month.

The station's astronauts have a list of tasks to work through and booting up their new "housemate" is some way down the schedule.

R2, as it's known for short, is a pioneer for its kind. Fifty years on from Gagarin's historic first for humans, the humanoid machines are following.

The robot's first operations will be very simple: a series of "games" on a board to demonstrate the performance seen on the ground can be replicated in the microgravity conditions experienced on the station.

JD Yamokoski is Robonaut Controls Lead from a company called , which is working on the Nasa project. He told me:

"Initially, we will be doing system check-out - minor things to earn our stripes. At first, these will be some free-motion tasks to make sure we don't interact with any objects on station we shouldn't. Then we'll move on to the taskboard. It's got a variety of switches, valves, and knobs, soft materials - the types of things you'd find all over station. We're going to interact with that taskboard and prove we can work with the same things humans work with. And then, over time, we have a series of upgrades we'd like to fly - everything from a battery so we can go wireless to a new mobility platform so Robonaut can move around station as opposed to sitting in one spot.
听
"As to the future, R2 will do anything that helps the crew out - all the dull and dirty jobs. For instance, on Saturday mornings the crew spend their time wiping down handrails on station. There are huge numbers of these rails. So Robonaut could help with the cleaning. We have full 3D models of the inside of the station and there are a number of ways we could program Robonaut to move around."

So, stage by stage, R2 is set to move on to bigger and better things. Its human-like hands and arms should allow R2 to pick up and work with the same tools the station crew use; and with the correct locomotive attachments, the robot will eventually just like the astronauts.

A double act: Humanoid robots will partner humans as we push out across the Solar System

It is easy enough to see where this is going, I think. Humanoid robots will increasingly work side-by-side with humans.

They will even stand in for astronauts during spacewalks or for those tasks in space thought too difficult or too dangerous for humans to accomplish.

And I wouldn't mind betting that at some point this century, they will actually lead their creators across the Solar System.

We often forget that Gagarin, Shepard and their ilk were preceded into Earth orbit by dogs and chimps.

Space: Sapientia, Populus, Audacia, Cultura, Exploratio

In the far more demanding quest to reach the asteroids, the planets and their moons, robotic humanoid sentinels could be playing very significant roles.

We wouldn't risk sending humans first to the volcanic fields of Io or to the icy lakes of Titan. The robots would lead the advance.

Not always humanoid forms, of course. But just as on station, which is made for humans, if the Mars camp is designed to be occupied by people then we may want to send humanoid robots to set up that camp and test it before the astronauts' arrival. JD again:

"The amount of computing power we have in R2 now is a testament to how far processors have come. The robot has got 30-40 computers inside it. As computers continue to miniaturise and become more powerful in that smaller package, what we can do with the robot will increase.
听
"Just as an example. You may have seen the IBM computer Watson that recently competed on the US TV quiz show Jeopardy. It's a large computer and its feat is that it can understand natural language. There's no doubt that in 50 years from now, the computational power that machine can harness will be shrunk to the size we can fit in something like Robonaut."

There will be some, of course, who will question whether humans even need to follow if the robots reach this expected level of sophistication.

The machines' requirements are fewer in terms of the resources needed to sustain them - they don't want for air, food, water, and the very narrow range of warm temperatures demanded by humans.

And, ultimately, the machines are expendable. They don't have to be returned - a necessity in the case of humans which only adds to the complexity and cost of space missions.

But robots cannot simply replace humans in future exploration. It's something I've been discussing of late with the .

He makes a passionate case for the human element in space exploration. Our need to reach out into the unknown is innate, and he uses a nice Latin mnemonic for SPACE which embodies this compulsion: Sapientia, Populus, Audacia, Cultura, Exploratio:

"We often ask ourselves: why do humans explore? There is no clear-cut answer to this; there is no mathematical proof. Going into space may be a technical endeavour but ultimately going into space is a cultural thing. And you can see that because we do it all around the globe, whether we're Americans, Europeans, Japanese or Chinese - going into space to explore is something innate to the human being.
听
"You cannot ask a robot about feelings. Let me use this example. If I go to anywhere on this planet and sit on a beach and watch the beautiful sunset. With my physics education I can explain to others where the colours come from and what those colours tell you about the composition of the atmosphere. Some people may not understand this but if I talk only about the beauty of the sunset, then they understand this. You cannot do this with a robot, because a robot can only provide you with answers that someone has pre-programmed into them earlier somehow.
听
"I'm not saying we should not send robots; this is not my point. The human ability to sense emotions and take them into account in our actions is unique. Now, there are many areas where emotions are not wanted and could be even a distraction, where robots can do a much better job than we can do."

You have to wonder sometimes whether it is a rollercoaster that Europe plans on sending to Mars rather than a rover 鈥� such are the ups and downs and the sweeping curves on its .

ExoMars: Another evolution beckons

The rover was originally envisaged as a small-ish technology demonstration mission which could show that Europe was able to land on the Red Planet, trundle around to interesting places, and drill beneath the surface.

The science would concentrate on looking for signs of past or present life. But the concept for achieving all this has gone through iteration after iteration.

Now we hear that the finished design for ExoMars, which was presented at the end of last year, will have to be re-written once more.

Engineers are being asked to scope something new 鈥� bigger perhaps, better perhaps, but something new鈥� again.

The idea of a European exobiology rover at the Red Planet was , and after a series of studies its formal implementation as a project was .

But almost immediately, the robot concept started to grow in size as the ambitions for what it could and should achieve also grew.

Soon, it was too big to fit on a Soyuz rocket and needed an Ariane or Proton launcher to send it on its way. And, as is often the case with complex space projects, its projected costs rose as well. I don鈥檛 think many of us were that surprised when its scheduled launch was , and , and .

The decision in 2009 of Nasa and Esa to merge their exploration programmes at the Red Planet offered a way out of this cul-de-sac.

For Europe, it meant the ExoMars rover could hitch a free ride on an American rocket in 2018.

The US wanted to send another rover of its own at that time, so as long as the two robots could fit into the same landing mechanism together everything ought to be fine.听But recent events have upset this tidy arrangement.

The US has decided the cost structure envisaged for 2018 simply cannot be afforded in the current fiscal environment.听

So Europe finds itself changing direction once again on ExoMars.

It is now proposed that the European robot and the American vehicle planned to accompany it in 2018 be combined into a single rover.

New drawing needed: 听The idea had been to send ExoMars and a US rover together on the same mission opportunity听

This new robot is likely to be substantially bigger than either of the two previous concepts.

It is being described as a 鈥淓uropean鈥� vehicle. It should incorporate all the instruments planned for听ExoMars, including the drill to go below the Martian surface. But it should carry some American instruments, and its manipulator arm will come from the US, as will a system to package 鈥� or cache 鈥� rocks.

Both Nasa and Esa have this idea that 2018 should be the start of 鈥淢ars sample return鈥� 鈥� the objective of bringing rocks back to Earth for study in the lab. In 2018 they will begin this process by finding the right rocks and packing them up. A later mission will be despatched to try to retrieve them.听

The key thing about this new-evolution rover is that it borrows heavily from the equipment designed for the upcoming . This is one way of keeping costs as low as possible.

MSL-Curiosity is big: It weighs about 900kg

Curiosity launches at the end of this year and is due to land in the August of 2012. I don鈥檛 know if you鈥檝e seen how this rover intends to get down on to the surface, but the idea is that .

Nasa and Esa want to re-use this architecture for 2018. Thefore, all of the landing gear 鈥� the entry capsule, the skycrane, and the tether system that does the actual lowering 鈥� will come from the US.

So there you go. All the design work in Europe that has been done since 2005 is going to have to go through yet another iteration.

Perhaps you鈥檝e been to an event in the UK where you鈥檝e seen a prototype of the ExoMars chassis 鈥� a six-wheeled trolley called either Bridget or Bruno. Well, put that to the back of your mind because engineers will soon have to produce another one to fit with new specifications.

Well in excess of 100 million euros has been spent on the ExoMars programme to date. Critics will raise their eyebrows at this, given the latest developments, but it would not be true to say all this money has somehow been wasted.

Much of the technology developed for ExoMars will find its way into the new vehicle.听But you would be forgiven if you had a little voice in the back of your head saying, 鈥渁re we nearly there yet?鈥�.

2018 is really not that far away in the context of space mission preparation. Engineers on both sides of the Atlantic are now going to have to crack on and deliver a workable concept.

It will be interesting also to see how much of the development of this vehicle is led from the UK.

Britain has committed 165 million euros to ExoMars to secure primacy for itself on the rover.

Will we now see a big, six-wheeled robot being assembled in the UK? I certainly hope so.

We鈥檙e a little bit clearer now in Europe on what the really big space science mission will be at the end of this decade鈥� just a little bit.

For the past four years, scientists and engineers have been developing three concepts that would cost European participating nations about a billion euros.听

IXO will no longer be the giant first envisaged, but still a major leap forward on current capability

To recap, they are: (1) a 20m-long that could see the very "edge" of a black hole; (2) a trio of satellites, collectively known as , which might be able to detect the ripples in space-time left by the moment of creation itself; and (3) a spacecraft that would visit the Jupiter system and go into orbit around the moon Ganymede. This one is called .

We were expecting the European Space Agency to give us a good indication this year of which mission might be the favoured one, with the launch pencilled in for 2020 or very soon after.

But as of today, the concepts as we know them 鈥� as they were presented to the scientific community in a big showpiece event in Paris in February 鈥� are now dead.听

Four years鈥� work and they鈥檝e hit a big buffer. They cannot be done as originally envisaged.

The reason is the Americans. In recent months, we鈥檝e seen two highly influential reports come out of the States which have attempted to summarise and prioritise current US thinking on space science.听

These reports 鈥� they鈥檙e called Decadal Surveys, for the obvious reason that they鈥檙e done once a decade 鈥� have put a mighty spanner in the European works.听

Europe had hoped to progress with one of its Big Three as a partnership with America.听

But the Decadal Surveys do not consider any of these concepts to align with the top-most US priorities in planetary science and astrophysics; and it鈥檚 quite clear from the budget situation facing the American space agency right now that there simply isn鈥檛 the money on the other side of the Atlantic to participate in them anyway 鈥� not at the level that was originally envisaged. Projects like the much-delayed James Webb Space Telescope have consumed huge funds.听

So what is going to happen?听

The IXO, LISA and Laplace teams have been told to go away and think how they could complete their missions as largely European-only ventures. They have just under a year to do this.听 听听

When they come back, their concepts will be smaller and they鈥檒l probably have new names, too.听

De-scoping the concepts and making them work for a billion euros may be easier said than done. 听

For Laplace, it looks more straightforward. In technology terms, we already know very well how to send a planetary probe to the outer planets. But Laplace was sold on the basis that it would deliver complementary science to an at another Jupiter moon, Europa. If its 鈥渃ousin鈥� isn鈥檛 going鈥�?

For a mission like LISA, a de-scoping is going to involve some head-scratching.听

It planned to fly three satellites five million km apart in an equilateral triangle formation. Laser beams travelling between the spacecraft would measure their separation very precisely.

The idea was that gravitational waves generated by exploding stars and merging black holes would wash over these beams and disturb them in a very characteristic way.听

It鈥檚 a new kind of astronomy that would allow you to study far-off phenomena without looking through a telescope.听

With perhaps just a billion euros to play with, the original architecture may not be achievable. 听One idea is to听still fly three satellites, but use only two laser 鈥渁rms鈥� to detect gravitational waves.听

Professor Bernie Schutz from the Max Planck Institute for Gravitational Physics, in Potsdam, told me:

"Within the European LISA community, we're kicking around lots of options. In fact, there are so many ideas I think it's pretty clear we will come up with some kind of design. We are asking ourselves key questions: what science can we keep, what will we lose, and are there some new things we could do? I say that because if we shorten the arms, for example, the frequency range changes, and that might open up new possibilities, new observational targets. We're quite certain we can come up with a design that will still make a persuasive scientific case. But it's really too early to say anything for certain."

With a descoped architecture necessarily comes a reduction in sensitivity and capability.听 Does LISA remain as compelling a venture as it once did?

This is the question that will face all three of the down-sized concepts when they are presented anew in 2012.

Professor Andy Fabian from Cambridge University, UK, is working on the IXO concept.听 He won鈥檛 now get the super-scope first envisaged but says the revised X-ray observatory will still be a marvel.听 He told me:

鈥漌e think we can come up with a mission which is a very significant advance on what we鈥檝e got already. It鈥檚 like the next generation of optical telescopes. Initially the European Southern Observatory鈥檚 next Extremely Large Telescope was going to be a 100m telescope, and then they went to 42m and now it may be just 30m.听 We鈥檒l be doing the same.听 We鈥檒l be smaller but we鈥檒l still be bigger than anything that has gone before.听 There are now lighter ways to make the mirror; there are higher spectral resolution spectrometers we can use, and also we will try to make this thing more restricted in its instrumentation. The original IXO concept had quite a range of instruments; we鈥檒l probably now only have one or two. We鈥檒l lose some possibilities, but in terms of the core observations 鈥� making spectra and images 鈥� I think we are going to have an enormous boost compared to what we can do at the moment. 滨鈥檓 quite bullish.鈥�

You can look at the positives to come out of this. It is an opportunity for Europe to stand tall and take a clear lead in certain areas of space science.

What Europe will hope, however, is that at least one of the trio will appear so attractive to the Americans that they will still want to come onboard.

This is not going to be at the levels previously considered, but it could reach $100m or more. Any additional money will mean more capability.听There will of course be many US scientists who are deeply disappointed that America can no longer participate in these missions as they had planned; and, as I understand it, efforts are being made to keep them involved听for the time being听as "observers".

The big cosmic elephant in this room is what Europe and the US decide to do at Mars, but I鈥檒l leave that for my next posting.

听