It’s now close to 15 months since NASA’s InSight lander arrived on Mars (see Space Sunday: insight on InSight for an overview of the mission and Space Sunday: InSight, MarCO and privately to the Moon for more on the mission and InSight’s Mars arrival). In that time the lander has completed a lot of science, but one thing has remained an issue: the HP³ experiment.
This is one of two surface experiments InSight placed on Mars, and comprises a base module and a long, slender self-propelled probe called the “mole”, designed to “burrow” its way down into the the sub-surface to a depth of up to 5 metres, towing a sensor-laden tether behind it designed to measure the heat flow from the planet’s interior. The mole has an internal hammering mechanism that is designed to drive it deeper into the ground, but this relies on friction against the material forming the walls of the hole it is creating – and this hasn’t been happening.
After a good initial start, the probe came to a halt with around 50% of its length embedded in the soil. At first it was thought it had hit solid bedrock preventing further motion; then it was thought that the mole was gaining insufficient traction from the hole walls, on account of the fine grain nature of the material it was trying to move through.
By mid-2019, engineers thought they had a solution: use the scoop at the end of the lander’s robot arm to compact the soil around the lip of hole in the hope of forcing sufficient material into the hole it would provide the traction the probe needed to drive itself forward. When this failed, the decision was made push the scoop directly against the side of the probe, pinning it between scoop and hole wall to again give the probe the traction it needed.
Initially, this approach worked, as I noted in Space Sunday: a mini-shuttle, Pluto’s far side & mole woes, but then the mole “bounced back”. Since then, the probe’s progress has been a case of “three steps forward, two steps back”, making some progress into the ground and then bouncing back – a source of much frustration among the science team.
After a year with the mole more-or-less “stalled”, mission engineers have decided to take more direct action. The decision has been made to try to “push” the probe using the robot arm’s scoop. This means placing the scoop on the top end of the mole – an approach that has so far been avoided out of concerns to might damage the sensor tether as it emerges from the same end of the probe. However, in manipulating the lander’s robot arm and its scoop over the course of a year, engineers are confident they can avoid harming the tether.
This latest effort to get the mole into the surface will take place in late February / early March. If it is successful, the team may revert to using the scoop to once again compress the sides of the probe’s hole to try to provide it with further traction as it continues to dig down into the subsurface material. Should the attempts fail, it’s unclear what might be tried to get the mole moving again; the mission team admitting they have “few alternatives” left to try.
How to Deflect an Asteroid
On April 13, 2029, an asteroid in the region of 370 metres in length and 45 metres across will pass by Earth at 30 km/s no further away from the planet’s surface than some of our geostationary satellites.
Called 99942 Apophis, an object I’ve written about in past Space Sunday articles, it is one of a large number of potentially hazardous objects – asteroids larger than 140 m in length that in crossing the Earth’s orbit as both they and the planet go around the Sun, pose a potential risk of one day colliding with us, with potentially devastating consequences. When it was discovered in 2004, initial tracking of Apophis suggested it could collide with Earth in 2029. Further observations of the object showed this would not happen, not would it do so the next times it passes close to Earth in 2036, 2068 and 2082.
Which is not to say Apophis or 101955 Bennu, or one of the many other PHOs – Potentially Hazardous Objects – that are being tracked might one day strike Earth. The tipping point for such a collision comes down to such an object passing through, or close to, it’s gravitational keyhole. This is a tiny region of space – perhaps only 800 metres across – where gravitational influences – notably that of Earth – are sufficient to actual “pull” an objects course onto a collision with Earth.
Currently, plans to try to prevent such an impact revolve around identifying when an object has passed its particular keyhole, making an collision inevitable. There’s a reason for this: identifying where an objects keyhole might lie isn’t a precise science, and relies on scientists known an awful lot, including things like the size, mass, velocity and composition of these objects, what forces might be at work to influence their orbit, and so on. However, by leaving things until after an object has passed its keyhole means the time available to try to divert it is relatively short, perhaps months or just a couple of years or so, leaving very little time to plan and execute a mission to prevent any such collision.
Better then, to identify when an object is liable to pass close enough to its keyhole that it it will be drawn into a collision path. This would provide a far greater lead time for planning how to deal with it. This is exactly what a team of MIT researchers are suggesting in a part that also defines a framework for deciding which type of mission would be most successful in deflecting an incoming asteroid.
Continue reading “Space Sunday: moles, asteroids and a high speed planet”
Inara Pey: Living in a Modemworld 