# ATV reboost homework: got answers?

If you enjoyed Rhett Allain's post last Friday as much as we did (see "Using astronaut Mike Fossum’s YouTube video to measure ATV acceleration"), then – like the rest of us here at the ATV blog – you're probably a bit of a space physics gearhead!

Therefore, you might enjoy reading (and answering!) a series of 'Reboost Homework' challenge questions that Rhett's posted over at Wired's dotphysics blog.

My favourite challenge question?

Assume the ISS has an acceleration of 0.03 m/s2 (this is the acceleration just due to the ATV reboost, not the gravitational acceleration). If an astronaut started in the Destiny module and let go, how long would it take to “fall” [as the astros are seen doing in the YT video] all the way to the back. You might want to look up this distance, but I think it is around 50 meters.

Interested? We'd like to invite all our ATV blog readers to answer any one (or all!) of Dr Allain's 'ATV Homework Questions'. Send us your answers, and we'll publish the best (or, at least, correct) ones as assessed by the ATV Operations team. The answer judged most imaginative will win a super ATV prize from our mission goody closet. Submit your own work only, please. All judging final. No cash value. One submission per entrant. Due date Friday, 3 May, 12:00 CEST.

Astronaut selection requires three fundamental tenets: health, brains, and experience. You have to be able to pass the toughest medical in the world, so stay in shape and eat right. You have to demonstrate the ability to learn complex things, so an advanced technical degree is needed. And you have to demonstrate good decision-making when the consequences really matter.

# Using astronaut Mike Fossum’s YouTube video to measure ATV acceleration

By Rhett Allain

The Automated Transfer Vehicle (ATV) doesn’t just bring supplies to the International Space Station. It can also be used for ISS reboosts. What is a reboost? In short, during a reboost, the ISS velocity is increased by a small amount to bring the space station up to a slightly higher orbit.

Why is this needed? Well, although the ISS is in space, there is still stuff up there (gas from the atmosphere) that exerts a small drag force on the Station, decreases its velocity. The reboost are there just to keep it where it needs to be.

This video shows the inside of the ISS during an ATV reboost, i.e. when the ATV's main thrusters were firing. Let’s see if we can estimate the ATV thrust based on the acceleration of astronauts inside the space station.

Rhett Allain

Editor's note: In addition to having a knack for science communication, Rhett Allain is Associate Professor of Physics at Southeastern Louisiana University. He writes regularly for Wired's Dot Physics blog and is a bit of a physics fanatic who spends more time than many pondering how daily life intersects with science. With the recently announced development of ATV in cooperation with NASA for Orion, we're delighted to feature a few posts from the far side of the Atlantic. Enjoy! – DGS

There are a couple of different ways you can measure the acceleration in NASA astronaut Mike Fossum's YouTube video, but I am going to use one of the astronauts themselves (we think this is the first scientific use of an astronaut's floating body as seen in a YT video to calculate ATV acceleration – Ed).

Basically, I will use a video analysis program (in this case, the free Tracker Video Analysis). With video analysis, you can get position and time data from each frame of a video. If the motion of the astronauts had been recorded from a side view, position vs. time would obviously be the best choice. As you can see in Mike's video above, however, Mike, astro Satoshi Furukawa and cosmonaut Sergy Volkov are moving away from the camera, so I will measure the angular size of a person.

As things move farther away from a camera, they also appear steadily smaller. Here is a diagram that shows the relationship between angle, size and distance.

If you know the angle theta (θ) and the length of the object, you can find the distance (which I call r) with the formula:

r = L / θ

With this, I can mark a point on each side of one of the receding astronauts as he accelerates away from the camera. With some basic estimations for the angular view of the camera (and size of an astronaut), I get the following plot of distance from the camera for one of the astronauts.

# So long… and thanks for all the oxygen

The ESA web portal published an article announcing the ATV-3 undocking and highlighting its mission success so far:

ESA’s ATV Edoardo Amaldi’s time is near. Next week the spacecraft will undock from the International Space Station and burn up in Earth’s atmosphere, its hugely successful mission coming to an end six months after launch.

ATV Edoardo Amaldi will undock during the night of 25/26 September, and, just 24 hours later, will be commanded to perform a controlled destructive re-entry high over an uninhabited area of the South Pacific.

# Update on today’s reboost – ATV-3′s last planned ISS burn

ESA's Daniel Firre has sent in an update from the Mission Director's console in ATV-CC Toulouse on this morning's ISS reboost – the final one planned for the ATV-3 mission:

The last reboost of the ISS by ATV3 has been successfully performed early this morning. The purpose of the reboost was to set up correct phasing for the Soyuz 30 landing and Soyuz 32 launch.

Post-manoeuvre evaluation of the orbit by the NASA trajectory specialists confirmed the following:

• Time of ignition was 05:05 CEST, with a total burn duration of 08 min 56 sec.
• ISS reached a delta-V of 1.28 m/sec, which in this case corresponds to an altitude increase of 2.23 km
• Propellant expenditure was in the order of 175 kg

ATV-3 now has almost no propellant left, apart of course from the reserve kept for the separation and reentry boosts, and a small margin in case a short-notice ISS debris avoidance manoeuvre

Best Regards,
-- Daniel

# ATV reboost: Station reaches 400 km altitude

Update from Daniel Firre at ATV-CC:

Exciting day today with such a big and complex reboost, involving two separate burns and switching tanks!

ATV fires its rocket engines for reboosting ISS to higher orbit

The second boost was just completed, nominally, with a measured delta-V  (change in velocity) of 4.9 m/s, which makes a total delta-V of 5.8 m/s for today's ATV propulsive support to ISS.

According to a preliminary update from the NASA navigation team, we have set a new ISS record here today, given that the entire ISS orbit is above 400 km altitude for the first time (perigee at 405km and apogee at 427 km)!

Of course, nothing comes for free; the fuel cost for today's double boost was close to 800kg, burned in 40 minutes of thruster firing!

Now it looks even further below...

# News from ATV-CC Toulouse: Today’s two-part ISS reboost continues

A quick update on today's dual-burn reboost from ATV-CC; ESA's Daniel Firre is on console at the Mission Director's position:

Today's reboost is split into two separate thruster ignitions. The purpose of the reboost is to set up the ISS phasing conditions for the Soyuz 30 landing in mid-September and Progress 49 accelerated rendezvous on 31 October.

Hot! Video showing how a 220N ATV thruster appears when firing. More details

The details of each part of the reboost are:

1. Time of ignition (TIG) 11:45:00 CEST. Burn duration (planned) is 6:24 min:secs providing a delta-V (change in velocity) of 0.9 m/s
2. TIG 15:17:00 GMT. Burn duration (planned) is 34:49 min:secs for a delta-V of 4.9 m/s

The total delta-V will be 5.8 m/s, which corresponds roughly to an increase in ISS altitude of 10 km.

Daniel Firre (right) in ESOC Main Control Room during Cryosat launch 8 April 2010

The propellant consumption for this reboost will be in the order of 780 kg.

The boost had to be split in two parts because the remaining propellant in one of the two tank systems of ATV-3 is not enough for the planned delta-V; therefore, it is necessary to switch tanks in between the two burns.

So far today, the first burn took place exactly as planned and ATV-CC has just performed the tank switching. Waiting now for the thruster temperatures to lower to the nominal value before starting the second burn.

... update after the second boost!

Cheers from Toulouse,

-- Daniel

# ATV-3 lifts Station today

The ISS is scheduled to perform two successive reboosts today using the Orbit Correction System thrusters on board ATV-3.

The first, at 11:45 CEST, is set to run for 6 min 24 seconds and provide a speed boost of 0.90 m/sec and 1.56 km orbital height increase. The second is set for 15:17 CEST (34 min 49 sec; 4.90 m/sec; 8.56 km, respectively).

The purpose of the reboosts is to set up the phasing conditions for the Soyuz 30S landing in mid-September and Progress 49P accelerated (4-orbit) rendezvous on 31 October.

# Update on ATV reboost anomaly

Editor's note: Yesterday's Station reboost resulted in an incomplete burn, which is explained below in an email received from ESA's Jean-Michel Bois, Head of Mission Operations at ATV-CC.

One ATV function is to maintain the ISS altitude by performing regular reboosts, raising the Station's altitude. This manoeuvre uses the ATV propulsion system, and is commanded by ISS software.

The regularly planned ISS reboost conducted by ATV-3 on 15 August stopped prematurely. The thruster burn was set to run for 1876 seconds to increase orbital speed by 4.4 m/s and raise the Station's orbit by 7.7 km to 414.4 km altitude.

The boost began as scheduled at 18:00 CEST using the No. 1 & 3 thrusters of the ATV vessel's Orbital Control System (OCS).

However, after achieving a 2.9 m/s speed increase, the boost was stopped by the ISS. A temperature alarm had been triggered by ATV on a thruster of the propulsion system (which was not used for this boost), but that is nevertheless permanently monitored.

This (correctly) generated an isolation of the suspect thruster from the rest of the vessel.

A signal was sent from ATV to the ISS to highlight this 'partial reconfiguration' (with ATV continuing to be available for the boost). But the ISS software stopped the boost, which was not the excepted reaction to this kind of anomaly.

Engineers at ATV-CC and their counterparts in Moscow and Houston are studying the cause of the initial ATV issue and of the unforeseen ISS reaction.

In order to give time to the ground experts to complete their investigation, it has been jointly agreed with the ISS control centres to perform the remainder of the yesterday's reboost during the next scheduled reboost slot, set for 22 August; this manoeuvre is compatible with the next vehicle (HTV and Soyuz) movements.

ATV remains in a safe configuration and is fully capable of performing any necessary operations, such as reboosting the Station or performing a debris avoidance manoeuvre if so commanded.

The ATV-3 Mission Manager, Massimo Cislaghi, said he was pleased with the skilled work of the joint ESA/CNES operations team in Toulouse together with the essential support of ESA Moscow in reacting to the issue and investigating the cause:

"While the results of the boost were 'outside routine business', the team reacted with skill to manage the issues that arose during the reboost, which are always delicate operations," said Massimo.

# ATV-3 reboosts ISS: view from ‘on console’ at ATV-CC

ATV-3 conducted its 6th ISS reboost manoeuvre early this morning, and ESA Mission Director Adam Williams oversaw the activity at ATV-CC, Toulouse. He's sent in a detailed timeline of how it went -- giving a rare, 'on console' look behind the scenes of ATV operations.

ATV fires its thrusters to reboost ISS to higher orbit

With high solar activity, there is an increased risk of highly charged particles affecting ATV, at worst causing a reset of the Fault Tolerant Computer. If this occurred during the reboost it would terminate the boost before it was fully completed.

However, the Houston space weather forecast was more positive [than that of CNES, nominally responsible for space weather monitoring for ATV - Ed.], and the trilateral [i.e. Houston, Moscow, Toulouse - Ed.] conclusion was that the reboost could continue. Moscow and Houston both agreed it was better to attempt a reboost, and deal with the consequences of any underboost if and when it happened.

Wednesday, 18 July 2012 - All times Toulouse local - CEST

02:00 - All teams are on console preparing ATV for the reboost. Everything is calm.

03:40 - Successful transition of ATV to 'ISS Attitude Control' mode.

05:15 - Successful transition of ATV to 'ISS Reboost' mode.

05:16 - Start of reboost...

05:35 - Successful end of reboost and transition back to 'ISS Attitude Control' mode. Delta-V (change in velocity) achieved was around 2.8 m/s, which raised the ISS approximately 5 km.

06:15 - ATV back in 'Dormant' mode. Time for an early breakfast!

# ATV-3 reboost update – Station orbits higher

Using its Orbit Correction System thrusters, ATV-3 performed a one-burn reboost of the ISS on 26 May at 02:10 CEST with a burn duration of 6 min, 17 sec. The burn achieved a 'delta-V' (change in orbital velocity) of 0.84 m/s (planned: 0.9 m/s), and increased the average Station altitude by 1.55 km (planned: 1.66 km).

Back in April, NASA astronaut Don Pettit, Expedition 30 flight engineer, captured this video of engines of the Automated Transfer Vehicle being fired to reboost the International Space Station. Credit: NASA

After the burn, the ISS was orbiting at 399.0 km average altitude, with 407.5 km apogee height and 390.6 km perigee height.  The reboost was a slight underburn, providing about 7% less than expected delta-V and altitude gain.

This reboost -- together with the next one in June -- will set up orbit phasing for Soyuz 29S departure and landing, set for 1 July (the flight that will bring astronaut André Kuipers back home -- Ed.).