Space Sunday: rockets and rovers

SpaceX is planning the maiden flight of its Falcon Heavy booster to take place in January 2018 – with an unusual payload. Credit: SpaceX

Elon Musk has announced the first payload that will be flown aboard the SpaceX Falcon Heavy, together with an ambitious goal in mind.

The maiden flight of the new heavy lift launcher had been expected to take place in December, as a part of an ambitious end-of-year five launch schedule. However, in tweets on Friday December 1st, 2017, Musk indicated the Falcon Heavy flight will now take place in January 2018. When it does, and if all goes according to plan, be sending Musk’s own car on its way to Mars – and possibly beyond.

Announcing the push-back on the Falcon Heavy launch

A car might sound a weird payload, but it is entirely in keeping with SpaceX’s tradition; the first Dragon capsule test flight in 2010 carried a giant wheel of cheese into space.

The first tweet on the launch also underlines Musk’s own uncertainty about its potential success; he has previously stated that he expects the first flight of the Falcon Heavy may end in a loss of the entire vehicle, simply because of the complexities of the system.

And the announcement about the payload and its (initial?) destination.

Comprising three Falcon 9 first stages strapped together side-by-side and firing 27 main engine simultaneously at launch means the vehicle will be generating a tremendous amount of thrust requiring all three stages to work smoothly together. They’ll also be generating a lot of vibration during the rocket’s ascent through the denser part of the Earth’s atmosphere. Only so much of this can be simulated and modelled; a maiden flight is the only way to find out where the remaining issues might lie.

However, if the launch is successful, it will be spectacular, involving the recovery of all three Falcon 9 stages to safe landings back on Earth. It will also boost Musk’s car towards Mars – which raises a question. Does SpaceX aim to orbit the car around Mars, or will the mission simply be a fly-by?

Elon Musk and his Tesla Roadser. Credit: Tesla.

Any attempt to achieve Mars orbit would require some kind of propulsion system to perform an orbital insertion burn, something which adds complexity to the mission. However, given Musk’s ambitions with Mars, placing even such an unusual payload into Mars orbit could yield valuable data for SpaceX. The car weighs 1.3 tonnes, so the total mass launched to Mars – car (likely modified somewhat, although the stereo will – according to Musk – be playing David Bowie’s Space Oddity during the ascent) payload bus, propulsion system, fuel, some kind of science system (why orbit Mars only to pass up the opportunity to gather data?) – could amount to around double that, if not more.

Musk’s comment about the payload being in “deep space for a billion years” seems to suggest the mission might by a fly-by, sending the car onwards and out across the solar system and beyond. Again, with a science payload sharing the space with the car, this could generate useful data. Either way the launch of such an unusual payload is likely to require additional US Federal Aviation Authority (FAA) approval; it will certainly require a launch license – which the FAA has yet to grant.

NASA Turns to Lunar Rover to Help With Next Mars Rover Mission

I’ve followed the Mars Science Laboratory (MSL) mission, more generally referred to as the Curiosity rover mission since 2012, tracking the discoveries made and the ups and downs of the mission. Overall, the rover has carried out some remarkable science and made a range of significant discoveries concerning ancient conditions within Gale Crater on Mars and the overall potential for the planet to have been able to potentially support microbial life at some point in its history.

But there have been hiccups along the way – computer glitches, issues with some of the rover’s hardware, and so on. These included was the 2013 discovery that Curiosity’s wheels were starting to show clear signs of wear and tear less than a year into the mission. The discovery was made during a routine examination of the rover’s general condition, carried out remotely using the imaging system mounted on Curiosity’s robot arm.

This image taken on April 18th, 2016 (Sol 1,315) by the Mars Hand Lens Imager (MAHLI) camera on the rover’s robot arm revels areas of damage on Curiosity’s centre left wheel, the result of periodically traversing very rough terrain since the rover arrived on Mars in 2012. Credit: NASA/JPL

The images captured of the rovers six aluminium wheels, each some 50 cm (20 inches) in diameter, revealed tears and a number of jagged punctures in one of them (above), the result of passage over the unforgiving, uneven and rock-strewn surface of Mars. While damage was not – and has not – become severe enough to threaten Curiosity’s ability to drive, at the time they were found, it did cause mission planners to revise part of the rover’s mission as it drove along the base of “Mount Sharp” near the centre of the crater, in order to avoid traversing a region shown from orbit to be particularly rugged. Since then, care has been taken to avoid exposing the rover to particularly rough areas of terrain.

As a result of the issues with Curiosity’s wheels, the team working on NASA’s follow-up rover mission, currently dubbed “Mars 2020” for the year it should arrive on the Red Planet, has been looking at alternative wheel designs for the rover. Physically identical to Curiosity in terms of over design, appearance, size and mass, but with an entirely different science capability, Mars 2020 was to have used similar wheels as well. However, the mission team has now decided to use a type of wheel rooted in the Apollo era.

The last three Apollo missions to the Moon in the 1970s (Apollo 15, 16 and 17), carried with them the LRV, or Lunar Rover Vehicle, a two-seat, electric buggy the astronauts could use to explore points of interest further away from their lunar lander than had been possible with earlier missions. The LRV used four independently driven wire mesh wheels mounted on rigid rims, and which could deform around and over small rocks and other surface features as the astronauts drove around.

The Mars Spring Tyre being tested over simulated Martian terrain, along with the current type of wheel using on the Curiosity rover, to compare handling / wear and tear between the two. NASA/JPL

Using the same basic approach to the LRV wheels, NASA engineers have developed the Spring Tire. It is made of hundreds of coiled steel wires made of memory alloys, woven into a flexible mesh. The latter, when assembled a certain way, allow the finished object to “remember” its original shape. This means the Spring Tyres are lightweight, able to deform under heavy loads and on rough terrain, and still cushion its hub and return to its default shape when returning to smooth terrain.

A further advantage over this type of wheel is the mesh surface offers far better weight distribution and traction when negotiating soft, sandy terrain. This has also proved to be an issue for Curiosity, which had to back-track out of a sandy valley when engineers noted it was having severe wheel slip issues that could either damage the rover’s drive motors if it became stuck in the sand, or might result in it teetering over. What was particularly ironic about this experience was that little valley in question had been selected as a route for Curiosity in order for it to avoid crossing much rougher terrain it was thought could further damage its wheels. Just how well the Spring Tyre handles rough terrain can be seen in the video, below.

Voyager 1 Fires Motors for the First Time in 37 Years

Voyager 1  the furthest human-made space vehicle from Earth celebrated the 40th anniversary of its launch in August 2017. The first spacecraft from Earth to reach the interstellar medium (although gravitationally speaking, it is still within the solar system), the probe is 141 AU (1 AU, or astronomical unit, equals the average distance between the Earth and the Sun) from Earth, and it is travelling at a velocity of 60,843 km/h (38,027 mph).

Although it is powered by a radioisotope thermoelectric generator (RTG), which generates electrical power via the radioactive decay of plutonium-238, the power source for the probe is not infinite. Because of this, systems on the vehicle were turned off as they were no longer needed, in order to reduce the amount of electrical power the vehicle requires. For example, shortly after Voyager 1 completed its fly-by of Saturn and was on its way out of the solar system, several of the science system – such as the cameras – were powered-down.

Another system powered-down, it’s job thought to have been completed, was Voyager 1’s trajectory correction manoeuvre (TCM) motors. An important part of the mission during the probe’s encounters at Jupiter and Saturn, they’d also fulfilled their role following the Saturn encounter and were turned off, leaving the craft to use its attitude-control thrusters to maintain a proper orientation in order to communicate with Earth.

The Voyager space probe. The TCM and attitude-control systems are located in the blocky spacecraft bus, behind the large communications dish. Credit: NASA/JPL

However, over the last couple of years, the performance of the attitude-control thrusters has been falling off, leading to concerns that communications with Voyager 1 would be lost should they fail completely without any back-up system to maintain the vehicle’s alignment with Earth.

To this end, it was decided to see if the TCM motors could be resuscitated and used as an alternative means of maintaining Voyager 1’s orientation. Doing so would not be easy; not only had the TCM systems been dormant for 37 years, they were never designed for the role, which requires short, pulse bursts of hydrazine gas, instead being intended for sustained, lengthy firings.

A team was assigned the task – which entailed trawling through assembler code line-by-line, determine what needed to be changed, write-up new instructions to allow the spacecraft to “wake up” the TCM systems, diagnose them, report back, and then carry out a test firing intended to mimic the kind of short, light bursts used by the attitude-control thrusters.

On November 28th, 2017, a command was sent to Voyager 1, ordering it to carry out a test firing of the TCM systems with a series of 10-millisecond pulses. The command took over 19.5 hours to reach the spacecraft, and a further 19.5 hours for the results to be received on Earth – be it in a reply (indicating possible success) or a complete loss of signal (indicating failure and the potential end of the mission).

As it turned out, a signal confirming the test was a success was received on Wednesday, November 29th, 2017. The plan now is to switch over to the TCM motors to handle spacecraft orientation, with the attitude-control thrusters being kept as a back-up and to give them a rest, hopefully extending their lifespan. However, given the extra electrical power load required by the TCM, operations will have to switch back to the attitude-control systems at some point in order to once again conserve as much power generation as possible and allow Voyager 1 to continue operating, possibly into the 2030s.

In the meantime, the Voyager mission team are looking into using the same technique with Voyager 2 in order to prolong the lifespan of its attitude-control systems.


Have any thoughts?

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.