(Note: Updated 6 May with comment on water transfer from Mike Steinkopf) ESA’s Daniel Firre sent in a note after lunch today (see our post immediately below – Ed.) with a summary/wrap up on some of the activities at ATV-CC this week.
The big event was today’s ISS reboost, which left the Station orbiting 3 m/second faster and over 5 km higher.
To prepare for the reboost, yesterday, NASA astronaut Don Pettit Don closed the protective shutters of the Destiny Lab, Node-3/Cupola and JPM (Japanese Kibo module) windows to prevent their contamination from ATV thrusters.
Reboost manoeuvre No. 3 took place as planned today at 10:37 CEST, “successfully and perfectly in line with planned operations,” writes Daniel. He reported:
The ATV’s propulsive support had a burn duration of 20:21 min:seconds, for a predicted and actual delta-V [increase in velocity] of 3.0 m/s (equals the ‘effort’ produced by ATV thrusters on the ISS complex). This resulted in an altitude raising of the station of 5.26 km… and left us with an ATV 392 kg lighter!
This reboost was needed to prepare/phase the ISS for the coming Soyuz 30 docking.
On 3 May, the team continued troubleshooting the first power chain of the ATV’s Russian Equipment Control System (RECS-1). Daniel says they got lots of data on the system and situation, and will continue troubleshooting. In the meantime, ATV is functioning nominally powered via the back-up RECS-2 chain.
Today, the crew is also scheduled to carry out a check of the functionality & performance of the Russian POTOK Air Purification System, which may have been involved in the loss of RECS-1 power feed from the Russian Service Module (to which ATV-3 is docked) to ATV-3 on 30 March.
6 May :: This update received from Mike Steinkopf – Ed.
Via NASA Daily Update 3 May: Kononenko set up the water transfer hose and pumping equipment and transferred water from Tank 1 of the ATV-3 WDS (Automated Transfer Vehicle 3 Water Delivery System) to a KOV EDV water container (#823). [The 40-minute procedure is specially designed for gas/liquid separation, i.e., to prevent air bubbles larger than ~10 mm from getting into the Elektron’s BZh Liquid Unit where they could cause Elektron shutdown.]
Mike adds:
One EDV (22 liter capacity) was filled using the pump unit in the Russian Service Module connected to the ATV Water Tank No. 1 via the ATV Water Delivery Panel. Aim was to fill the Elektron with water. Best regards,
— Mike Steinkopf
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Discussion: 3 comments
I guess I do not understand the results of the reboost. It is stated that the velocity was increased by 3 m/s and the altitude was increased by 5.26 km. These numbers do not appear to be consistent with maintaining a circular orbit. If the altitude were IN-creased by 5.26 km, the velocity should have been DE-creased by 3 m/s since higher orbits have lower velocities. If I do the calculation, I tend to get those numbers, but with opposite signs. I suppose one could increase the eccentricity with an increase in velocity and apogee, but that still leaves a portion of the orbit at low altitude and would seem to defeat the purpose of the reboost. What is the resolution to my confusion?
Also, what was the thrust of the ATV engines for the 20 minute period? I do not know the ISS mass for certain so it is a bit difficult to calculate.
I would ppreciate your relieving my confusion.
Hi Gene: Thanks for your query; we’ve passed it along to the right folks here and I’m hopeful we’ll get an answer shortly. Cheers! — Daniel
The stated data on the orbital re-boost are correct.
Each main engine of the ATV delivers a thrust of 490 N. Two of them are fired in parallel, raising the effective thrust to 980 N. Assuming a combined mass of ISS plus attached ATV and Soyuz craft of around 400 t (I don’t have the actual value handy but it should be around that) and a stated manoeuvre duration of 20’21”, the imparted delta-v works out almost exactly as 3 m/s.
If the delta-v is imparted in the direction of orbital velocity, i.e., “making the object go faster,” it increases the orbital energy and counteracts the accumulated dissipative effect of atmospheric drag.
A delta-v of 3 m/s, if imparted on a near-circular orbit at around 400 km altitude, changes the semi-major axis (i.e., the mean altitude) by exactly the amount mentioned in the article. The obtained orbit will likely have a small eccentricity, but also the orbit before the boost was not perfectly circular, and placing the manoeuvre appropriately can avoid having an unwanted eccentricity build-up.
The fact that the spacecraft is accelerated by 3 m/s, applying this delta-v in the direction of orbital motion, does not imply that the actual orbital velocity increased. It is a well-known paradox of astrodynamics that if one accelerates a spacecraft, thus putting more energy into its orbit, it will end up on a higher orbit where its speed is actually lower.
Conversely, if one brakes down a spacecraft, e.g., by the continuous action of atmospheric drag, it will end up on a lower orbit where its velocity is higher. It may seem counter-intuitive, but that’s the way it is.