Sci-Fi Shorts: Space Debris

Space Debris

By Andrew Doubt

She feels like a speed cop as she checks the ranging equipment, watching it sweeping systematically across possible approach trajectories; or perhaps a parish councillor trying to catch local youths speeding through a village; how long before they discover her speed gun’s actually a hairdryer?  She smiles: this task is almost as therapeutic as her daily, three-hour exercise sessions aimed at reducing bone and muscle loss.

 

The equipment was a last-minute addition to her research tasks and does not take the intense concentration needed for tasks done suited-up outside; she allows her mind to wander.  She keeps half an eye on the interim readouts, giving the diameter, distance and velocity of each object detected.  This is a Mars-craft prototype, for use beyond the solar system.  An algorithm generates an orange warning for objects needing closer monitoring, and a red alert for those requiring immediate evasive action; there have been no warnings in the first three weeks of testing.

 

She enjoys working up here, in spite of the cramped conditions and the substantial risks: a one-in-forty risk of death on launch or re-entry.  During selection, she scored highly on equanimity: persistence, patience, an easy tolerance of the other five on board and an ability to put the mission first.

 

About once a year, the crew gets instructions from ground surveillance to use their thrusters to change altitude, as a debris avoidance manoeuvre; if the debris is small, or spotted too late, the crew repairs to the better-shielded Russian module until it has passed.  And four times in the twenty years of operation, the crew has had to wait, suited-up, in the Soyuz spacecraft until the danger was over.  She’d enjoyed the film “Gravity”, as the physics was mostly pretty accurate, but it had really exaggerated the actual amount of space junk at orbital height.

 

There’d be less debris en route to Mars, but potentially higher-velocity objects coming from elsewhere.  She hopes the prototype’s working well enough to give the station prior warning of ground instructions; detailed cross-checks against ground measurements she’s leaving to the ground team.

 

It’s funny how the mind picks out groups of numbers in a random sequence and looks for coincidences; that’s the second time she’s seen the digits of her three children’s ages in chronological order.  At least they’re old enough for their father to look after them, and they are proud of her.  At school, she’d noticed groups of three; interest in patterns had reinforced her interest in maths, and had eventually led to her career as an astronaut.  Now she was up to groups of six – she should really try to turn that off: it was becoming distracting.

 

The equipment continues to pick up various objects, down to quite small diameters, and quite far out; this session to date, there’ve been some hundred and twenty objects of sufficient size and velocity to do damage to the station, and within the range of the detector, but none has been assessed as being on a possible collision course.  She’s looking forward to her leisure break, when she plans to check through the data.  That’ll put paid to the coincidence patterns.

 

*

 

Suddenly, an orange warning is displayed, the first there’s been; an object has been tagged.  The display showing its diameter seems familiar – were the digits not the same as an earlier object?  She knows the size distribution of objects should follow a power law: lots of small ones, reducing in number with size, and the very occasional, extremely large one, so-called ‘black swans’.  Maybe two identical diameters during one measurement period is not so unusual, if the objects are small; this one’s about half the size of a golf ball.

 

The distance of the tagged object corresponds to the extreme range of the equipment, around 4 million kilometres.  Her equanimity is startled by the speed displayed: 800km/s.  The equipment now has 100% of her attention.  This is one third higher than the highest speed measured for any object in the solar system, whether comet or asteroid, and is well above escape velocity, meaning it would not be confined within the solar system, and could even have come from outside.  The detector seems to be working OK.  She plots the object’s calculated trajectory.  It will intersect the path of the station, heading directly downwards towards earth, one minute before the station gets there, following its next 90-minute circuit of the earth.  At that speed, it would punch a complete hole right through the station wherever it hit.  Thankfully, one minute away at station orbital speed means a good 400km miss.

 

While pondering this, she idly checks the session data for other objects with the same diameter.  There is one.  Her tic was right.  It’s exactly the same as the first one, same diameter, same speed, same direction, and only 100,000km, or two minutes of travel, closer than the other.  Similar trajectory, crossing just three minutes before station arrival, a 1200km miss.

 

Reality wobbles, briefly.

 

Somebody’s put a bug in the data?  She re-checks all the equipment.  A memory of firing two consecutive barrels at a clay pigeon shoot flits through her head.  She slows her breathing, starts searching the rest of the data, and stares for a long time at an earlier part of the data.

 

Everything goes still.

 

*

 

“I asked the Captain to call all of us together urgently.  I have a problem that’s churning my brain.  It has a potentially fundamental impact on our survival.  I want you to check my logic, my reasoning, my sanity, before we contact Control.

 

“The ranging equipment we are developing for the Mars craft appears to have detected two pairs of small, very-high-speed, rock-like objects heading towards us along a line that extrapolates back towards a part of the galactic disk with a high density of stellar systems.”

 

Come on!  You can get aligned debris from a comet break-up.

 

“No, these four objects are identical, to the measurable accuracy.  I have triple-checked the equipment and can find no fault.

 

“The first pair crossed the path of the station earlier today, at points approximately seven and five minutes, respectively, ahead of our arrival there.  The second pair is predicted to cross our path three minutes and one minute, respectively, before we arrive, in just under an hour’s time.  If the prediction’s accurate, neither of the second pair will collide with the station.”

 

Why has the equipment only alarmed the fourth object?

 

“Because the collision-avoidance distance adopted for the detector is 1000km.”

 

Why has Ground Control not detected these objects?

 

“I don’t know, but it may be because the objects are small.  And the four of them will cross our path over a ninety-minute period around midday over the Pacific, where the burn-up trail will be least obvious from the ground.  The projectiles are also light in iron, so they will more likely burn up in the atmosphere and, if they don’t, they’ll end up in the ocean.

 

“Carl Sagan compared space debris falling to earth to a cosmic shooting gallery, where the space station is one of the ducks.  I feel like one of the ducks.  If, after our next earth-circuit, we detect a third pair of objects coming from the same direction, and their trajectories are predicted to cross ours one minute and three minutes after we do, I will start quacking.”

 

Carl Sagan was a well-known extra-terrestrial obsessive!  Ignore him.  At that time, the first pulsar was thought to be artificial.

 

“This evidence would be much more compelling: six equally-timed projectiles.

 

“A scenario: it’s a hundred years since we started broadcasting electromagnetic waves to the rest of the universe.  It’s twenty years since this space station, earth’s largest artificial satellite, was launched.  That’s about the time we started detecting earth-like exoplanets orbiting nearby stars.  A similar technique could be used to observe us from, say, the exoplanet Proxima Centauri four light-years away; something might notice the station start up and decide to shoot it down.  They would need to dispatch a projectile launcher into the solar system at an average journey speed 30% of the speed of light (including acceleration and deceleration).”

 

But that’s way beyond any conceivable technology.

 

“No: US-funded Breakthrough Starshot is projecting 20% light speed, violating no currently known laws of physics.  It’s conceivable.  After a hundred years of fast technological development, we can still only see and explain 5% of the universe.  We have no idea what ‘dark matter’ or ‘dark energy’ are.  An older civilisation might have.

 

“But why would something want to treat us as a clay pigeon?  Are we space debris?  Is it a passing space vessel out for some sport?  Perhaps they find us inferior.  If the third pair is as I predict, the projectiles will miss.  Is that intentional, or is their feedback limited at extreme distances?  Is it a test to see whether we notice and how we react?

 

“So, what now?  Do you need to lock me up?  What shall we tell Control?”