The Service Module Will Soon Join the Space Station

By Keith Cowing
June 29, 2000
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Service ModuleNASA presented a briefing on Wednesday, 28 June 2000 regarding the upcoming launch of the Service Module on Mission 1R. If all goes according to plan, launch will occur on 12 July at 4:56 GMT (11 July 11:56 PM CDT). The launch date for the Service Module was formally set in Moscow on Monday at the General Designers Review (GDR).

This Service Module launch date depends upon a second successful launch of a Proton booster (carrying a Russian military satellite) using redesigned engines. This second Proton launch is expected to occur on 6 July. The Service Module launch window extends from 8 to 16 July with the ability to reschedule launches on successive, alternate even dates (i.e. 8,10, 12 July etc.)

A Much Needed – and Delayed Capability

When Space Station Freedom was redesigned in 1994 and transformed into what eventually became known as the “International” Space Station (Freedom was quite “international” before the redesign), the bulk of the orbital reboost and resupply responsibilities, previously a U.S. task, were taken on by Russia.

The Service Module (also known formally as “Zvezda”) is the first element of the International Space Station to be launched that was built and paid for by a country other than the U.S. Although the Russian-built FGB (“Zarya'”) has been in space as part of the ISS for more than a year, it was paid for by the U.S.
The FGB (Functional Cargo Block) was designed to provide initial reboost and limited guidance, navigation, and control capabilities until the Service Module arrived.

The Service Module is designed to provide the ISS with life support, reboost, attitude control, EVA, and communications capabilities. It will also provide power to the Russian segment of ISS. According to the original assembly sequence for the redesigned space station in 1993, the Service Module was supposed to have been in orbit in April 1998. However, a series of delays, caused mostly by Russia’s continued inability to generate the funds required to pay for the Service Module, pushed the launch date back by more than 2 years. The continued delays forced NASA to come up with several contingency plans – plans which themselves have been plagued by delays and cost overruns.

The Service Module’s launch was delayed even further when the Proton rocket fleet suffered two launch failures. The failures were eventually traced to manufacturing problems within upper stage rocket engines. These engines have since been redesigned. According to an agreement between Dan Goldin and RSA chief Yuri Koptev, there will be two flights of Protons utilizing the redesigned engines before Russia will commit to launching the Service Module on a redesigned Proton booster.

Russia is very confident that the second Proton launch with redesigned engines will be as successful as the first. According to NASA, the second Proton launch will happen at around 3:00 AM local time. The Service Module is scheduled to be mated to its booster on 6 July and arrive at its at its fueling station by railcar at the Baikonur Cosmodrome at 8:00 AM on that very same day that the military Proton launch occurs. NASA has expressed every confidence – as have the Russians – that the military Proton will launch on time and that preparations for the Service Module launch will begin promptly at 8:00 AM. The Service Module and its Proton booster will then be moved to Launch Pad #23 on 7 July for final launch preparations.

The Launch Window

There are two main constraints driving the selection of the Service Module’s launch window . The first is to have the docking occur in sunlight over Russia. Russia uses a television system to monitor the entire docking process and sufficient lighting is required for the TV cameras. The other constraint has to do with the beta angle – the angle between the sun and a spacecraft’s orbital plane. A beta angle of less than 30 degrees is required so as to make sure enough power is generated by the Service Module’s solar arrays to allow docking to occur with an adequate reserve margin. Docking and other critical activities requiring ground interaction also need to happen while the spacecraft is actually flying over Russia due to Russia’s lack of satellite coverage.

Docking Overview

Service Module Engine BurnDocking between the Service Module and the ISS is scheduled for 26 July at 1:10 GMT (8:10 PM CDT 25 July), 14 days after launch. The reason why it takes two weeks to actually dock is rather straight forward. Once the final docking process begins, the Russians want to be absolutely certain that the process is not gong to be interrupted by a technical glitch. With only enough fuel for two, perhaps three docking attempts, the Russians want everything to be in perfect condition. As such, the two weeks prior to docking allow a thorough series of on-orbit checks to be conducted with additional unscheduled time held in reserve to deal with contingencies that may arise.

Once docking is completed, and the ISS is checked out, a Progress logistics vehicle will be launched. This will occur no earlier than 29 July , three days after docking between the ISS and the Service Module. The Progress vehicle would then dock with ISS on 2 August. This would be followed by the STS-106/2a.2b Space Shuttle mission on 8 September. Another Progress flight will follow in September setting the stage for the arrival of the Expedition 1 crew on 30 October.

Events Leading Up To Docking

The following is a short list of the significant events during the initial portion of the Service Module’s mission leading up to docking listed by Flight Day (FD):

  • FD1 – launch , antenna and solar array deployment, activate Guidance, Navigation, and Control activation.

  • FD2 – perform test burns on with the main engines ; solar array tests; use horizon sensors to update onboard computers

  • FD3 – perform a large reboost burn – so called ” Interval 1″ set of burns. If the launch of Service Module was done according to plan, an attempt would be made to place it in a 357 km high orbit where the ISS is. However, if the Service Module’ s launch used more fuel than planned, the first burn would place it in a 350 km high orbit and the ISS would drop its orbit (by doing a retrograde burn) to meet the Service Module. At one point the Service Module would do a fly by of the ISS.

  • FD4 – additional orbit correction burns and communication system checks.

  • FD5 – tests of Guidance, Navigation, and Control systems.

  • FD6 – test of the television system

  • FD7 – nothing scheduled

  • FD8 – passive cooling system test for avionics

  • FD9- nothing scheduled

  • FD10 – test of solar arrays

  • FD11 – Service Module docking test . This will include a run through of all of the events that will occur on docking day. This will include a test of the docking mechanism

  • FD12 – Interval 2 set of correction burns designed to phase the Service Module with the ISS

  • FD13 – last minute course corrections

  • FD14 – final last engine burns by either the ISS or SM, as needed

  • FD15 – docking

  • FD16-18 check of vestibule that connects the Service Module and the FGB including pressurization checks

  • FD19 – connect the computer systems aboard the Service Module with those already operating the FGB/Node (ISS)

    Docking Day – In Detail

    Service Module docked to ISSOn FD15, “docking day”, final events begin over Russia two orbits prior to the actual docking. This sequence of events begins with the first of two final correction burns, both of which occur autonomously without intervention from the ground. The second burn is performed 45 minutes after the first and serves to circularize the Service Module’s orbit.

    One orbit prior to docking, the ISS will become the active partner in the rendezvous and docking process. The Service Module now waits for something (the ISS) to come up and attach to it. The KURS automated rendezvous and docking software and hardware will be then be activated and checked out to sure that it is working. Eventually, the Service Module and the ISS will start to talk to each other and coordinate their motion with respect to one another.

    When the Service Module and the ISS are 5 km apart, closing at a rate of 1 meter per second, the docking process will transfer to short range guidance mode as the distance is narrowed down to 300 meters. At this point the ISS will be located above Service Module. The ISS will eventually move to a position behind the Service Module where it will stop at a distance of 200 meters. A switchover from omnidirectional to directional antennas will then occur thus allowing both allow vehicles to talk with one another and exchange very accurate range information. When all systems and positions are verified, a command will be sent from the ground and docking will occur autonomously.

    When an indication has been received that contact has occurred, the FGB’s control systems will be shut down. The docking probe will then retract and clamps will drive from the Service Module into the FGB. The Service Module’s solar arrays will then start to track the sun again maximizing available power.

    The newly expanded ISS will then orbit the Earth once in “free drift” mode while everything is checked out. Once this is done, and everything is OK, remaining clamps between the Service Module and the FGB will engage. Once docking is complete three days of leak testing and other verification procedures will occur.
    At one point computers in the Service Module and computers in the ISS will become fully integrated. This is important since the Service Module is designed to assume control of the entire ISS. The FGB, which had been controlling the ISS up until now will henceforth have its systems controlled by the Service Module.

    STS-106: Incorporating the Service Module into the ISS

    Cosmonaut Yuri Malenchenko, Mission Specialist on the upcoming STS-106 mission, provided a description of his crew’s mission. The main task for the STS-106 crew is to prepare the ISS such that first crew (Expedition 1) can live there. Among the first tasks will be an EVA that will last between 5 and 6 hours during which U.S. and Russian systems will be connected. Power cables will be connected between the FGB and the Service Module and ORLAN cables will be installed to support future EVA activity on the Russian segment. This EVA will be done using U.S. spacesuits but will involve work on the Russian segment using Russian equipment – another indication of the growing integration of U.S. and Russian hardware, systems, and operations.

    On mission day 5, the crew will begin to activate a number of dormant systems on the ISS. Hatches will be opened and the crew will enter the Service Module for the first time. This will be followed by the routing of air ducts, the activation of the Service Module’s life support systems, and activation of Caution and Warning systems. In addition, the treadmill/ergometer, packet communication computer, storage batteries, and toilet will all be installed.

    The Progress cargo vehicle (which docked in early August) will be unloaded, refilled with unneeded material, and then prepared for undocking. Some frames and brackets used only during the launch of the Service Module will be disassembled and prepared for disposal. On mission day 9 the hatches will be closed and preparations for the return to Earth will begin.

    Contingencies – Minor and Large

    Should a contingency arise once the Service Module is joined to the ISS, a demonstrated ability to use the Russian segment (Service Module/FGB) to control the US segment (Node 1) and vice versa is available. During the time that the ISS (composed of the FGB and Node 1) orbited waiting for the Service Module, a number of instances occurred where U.S. and Russian controllers had to improvise and use one system to control another. This happened when some failures occurred within Node 1. U.S. controllers were able to monitor the health and status of Node 1 via the FGB. Conversely, since the Russians currently do not have satellites that allow them to directly communicate with the ISS at all times, they can use U.S. systems to command and monitor their modules.

    If the docking is not successful on the first attempt at least one more attempt is possible. Depending on the fuel used additional attempts may also be possible, however the amount of fuel available is limited. Should the docking not be accomplished, a specially trained Soyuz crew (“Expedition Zero”) will be on stand by for launching on short notice. Should the crew be needed they would likely be launched on or around 10 August.

    The Expedition Zero crew would dock with the Service Module and then manually dock the Service Module/Soyuz with the ISS. Once this is accomplished the crew would then see to some of the tasks originally assigned to the 2a.2b crew – i.e. establishing life support systems and other procedures so as to allow the crew to live aboard the Service Module and to prepare and check out the ISS for the subsequent visit by the STS-106 mission. Should the contingency Soyuz mission be required, the expectation is that the crew would return to Earth on 28 August. The assembly sequence would then be resumed with the launch of STS-106 /2a.2b on 8 September, a Progress launch on 20 September, and launch of the Expedition 1 crew aboard a Soyuz on 30 October.

    The question arose as to what NASA would do if the Service Module was lost during launch. NASA was pressured into developing contingency plans several years ago when Congress grew impatient over program delays, Russian funding shortfalls, and a lack of clear contingency options should major components be lost or damaged. Two solutions eventually emerged. The first was the Interim Control Module (ICM), a variation upon existing hardware developed by the Naval Research Laboratory for classified military systems. The ICM is only designed as a stopgap measure. One would be flown and left on orbit for a year or so. It would then be replaced with another module. According to NASA there are plans to fly the ICM as early as April 2001. The ICM can be used to provide most of the reboost support for early configurations of the ISS, but not for the larger configurations the ISS will have in later years.

    The second contingency is the U.S. Propulsion Module (USPM) which was designed to replace the Service Module’s reboost capabilities should Russia be unable to meet its resupply responsibilities. Unlike the ICM, the USPM would be capable of all of the reboost and control capabilities the Service Module is capable of providing. However, the USPM will not have pressurized living quarters. Nor it will apparently have the on-orbit refueling capabilities that the Service Module has.

    The launch of the USPM has slipped steadily from its original 2001/2002 date as its projected cost have increased. Depending on which sources you refer to at NASA, the USPM could be launched in 2003 or as late as 2005. NASA is currently entertaining a rebid on the construction of the USPM in an attempt to hold down costs and enhance the delivery date. Meanwhile, the General Accounting Office has been requested to audit the USPM project as the result of a joint Congressional request from the Senate and House. The results of this audit could take the better part of a year to complete.

    Should the Service Module be lost, the ICM would fill in for the Service Module’s reboost capabilities temporarily. NASA would work to upgrade the FGB (already well past its original certified operations period) so that it could last even longer. There would also be pressure to get the U.S. Lab module into space such that the CMGs (Control Moment Gyroscopes) could be used as a non-propulsive means of controlling the ISS’s orientation, thus decreasing the need for fuel. There might also be a push to advance the installation of life support hardware planned for the U.S. lab to Node 3.

    The assembly sequence would then be put on hold somewhere around flights 5A or 6A until either the U.S. Propulsion Module or a back up Service Module could be put into space. Given recent delays in the USPM program, and chronic Russian money problems, this could take several years.

    Critical Path Issues and Russia’s Capabilities

    When asked if the Russians are still going to be in the critical path once the Service Module is launched, NASA avoided making a direct answer. They cited the fact that there is still a requirement for the Russians to provide Soyuz vehicles as crew return vehicles until such time as the X-38 becomes operational. Given delays in the X-38 program this could cause problems.

    When asked how few Progress resupply flights the Russians could get away with making and not hamper the program, NASA responded that the planned rate is 6 per year with each mission carrying 4,000 pounds of dry cargo. The Space Shuttle could make up some of the cargo requirements, and perform some reboost (using its Orbital Maneuvering System engines) but could not carry propellant to refuel the Service Module. As such, 3 Progress flights a year would be the lower limit that could be flown without significant impacts to the overall program.

    The question of Russia’s ability to meet its commitments in the face of distractions raised by commercial activities (i.e. Mir) came up. NASA responded that Russia does not lack the manufacturing capability to produce Progress and Soyuz vehicles. What it does lack, though, is the cash to pay for materials required to manufacture these vehicles. Without getting into much in the way of specifics, NASA seems to hold out some hope that some unspecified “commercial” alternatives may alleviate this problem.

    Mir and The Service Module: Close Cousins

    Another question involved the design similarities between the Service Module and Mir’s core module. The Service Module is an upgraded version of the Mir Core Module. Indeed, at one point, it was supposed to have formed the core of the Mir 2 space station. When asked how the two modules differed, NASA replied that one of the main differences was the computer system aboard the Service Module. The central computer used on the Service Module was manufactured by DASA and provided for use on the Service Module by ESA.

    While most of the computers used on the ISS are of late 1980’s Intel 80386 processor vintage (hardened for space applications), the Service Module uses a Sparc 10 design that is only 6 years old. Indeed, according to NASA, the Service Module’s computer system is actually a bit more up to date than the systems provided in the U.S. segment of the ISS.

    The Service Module has also enhanced the telemetry, command, and guidance, navigation and control systems and has adopted the 1553 data bus standard that is used on the other portions of the ISS. In addition to the computer and avionics upgrades, Russia has also updated the notorious oxygen candles (SFOGs) that caused the fire on Mir so as to be safer and more reliable. In addition, the ventilation system has been upgraded as well.

    Safety Issues

    Another question was asked regarding the fact that the Service Module does not meet some ISS program standards for safety and crew comfort. The Service Module’s interior (as well as that of the FGB) has a variety of noise sources that combine to raise noise levels above the crew requirements levied upon the ISS. This is a problem that has plagued Mir and earlier Russian space stations.

    NASA’s plan is to begin modifying the Service Module on Flight STS-106/2a.2b to reduce the noise. Crew sleep stations will be installed which offer comparatively quiet locations. Ear plugs and active noise reduction headsets will be left aboard as will noise measuring devices. Further quieting will be done by the Expedition 1 crew using acoustic baffling hardware launched on Progress vehicles. NASA has offered to loft some of these items earlier on Shuttle missions – an option under consideration by Russia.

    The Service Module also lacks sufficient external shielding to meet the ISS program’s micrometeoroid and orbital debris requirements for resisting hull puncturing. NASA will launch new shielding for installation on the Service Module on Shuttle Mission 7a.1 and will finish up the delivery and installation of the shielding on flights 1JA and 14A.

    Almost There

    All told, NASA seems to be confident that the Service Module will be launched on time and that it will successfully dock with the International Space Station. A number of people at NASA – and at the other participating space agencies – are clearly eager to get on with the assembly of the ISS – as well as its utilization. A huge collective sigh of relief is certain to be heard in mission control centers around the world when the Service Module is safely attached to the space station.

    Related Links

    ° Next Space Station Component Presses Toward July Launch Date, NASA

    ° International Space Station Status Report #25, NASA

    ° Europe’s first Space Station hardware set for launch on board Zvezda module on 12 July, ESA

    ° Service Module to be Launched on 12 July 2000, SpaceRef, 26 June 2000

    ° NASA Sets Launch Date for STS-101 to Keep the FGB Alive, SpaceRef, 31 January 2000

    ° NASA quietly Moves to Adjust ISS Schedule to Accomodate Yet Another Service Module Slip, SpaceRef, 28 January 2000

    ° Proton Launch Failure Report Released, SpaceRef, 10 January 2000

    ° Space Shuttle Launch Schedule for 2000 ISS Missions Under Review, SpaceRef, 4 January 2000

    Background Information

    ° International Space Station, SpaceRef Directory

    ° Zvezda Service Module, NASA JSC

    ° Zvezda Press Kit, NASA JSC

    ° Zvezda Launch Countdown, NASA JSC

    ° Service Module images, NASA JSC

  • SpaceRef co-founder, Explorers Club Fellow, ex-NASA, Away Teams, Journalist, Space & Astrobiology, Lapsed climber.