Space Station Option A Technical and Utilization Audit July 1993

Source: Space Station Freedom Program Office

President Clinton chose Option A as the preferred design for the space station based upon the Vest Committee report. In doing so, the president gave direction to NASA which included adding portions of Option B such as larger modules, truss modifications, and data system simplifications to the Option A design. Such direction has also been clearly expressed by Congress.

According to the presentations made by the leader of the Option A team at Marshall Space Flight Center on 29 June 1993, Option A management was still under direction to pursue Option A1. At this meeting, it was made clear by Option A management that using design features from Option B (Freedom) was not going to be entertained. Indeed, any such attempt was vigorously discouraged. Persons making such suggestions were removed from the participation lists for subsequent discussions at the space station redesign offices in Crystal City.

Option A's main selling point was a space station design that used Space Station Freedom-developed hardware, with deletions and simplifications to significantly cut costs. The cost savings claimed by Option A's modifications to Space Station Freedom's hardware are unfounded and will be outweighed by the costs and schedule delays needed to try and make the designs work in an Option A configuration. These costs have not been included in the Option A presentations to the White House and Congress. When these costs are added to the advertised cost of Option A, Option B (Freedom) begins to look like a bargain.

If such design changes are not made to Option A, a space station design will emerge which will require hundreds of millions of dollars in additional funding and will experience schedule slips which will delay the deployment of a research facility (of dubious value) until the end of the century. Funding for the space station program barely escaped defeat for FY 1994. After hearing that an additional $2.1 billion of FY 1994 funding has produced an underdesigned, over-budget space station, a Congress presented with the aforementioned problems will certainly be less charitable when considering the FY 1995 budget request from NASA.

And then there will be no space station at all.


1. Payload accommodations (internal and external) are either unspecified or reduced to the point where utilization of this Option A space station is questionable. Using the Option B (Freedom) items listed below plus the payload hardware items deleted in Option A will bring utilization capabilities up to the point where meaningful science can be performed.

2. The common laboratory modules proposed by Option A have severe weight problems which will prevent them from being launched without expensive (and uncosted) modifications to the Space Shuttle. Using the Option B (Freedom) Lab/Hab modules and nodes will resolve this problem.

3. The modifications to the external truss structure proposed by Option A will not work with the current Space Station Freedom designs. Virtually the entire truss system will need to be redesigned. Deletion of the Alpha joint degrades power generation and microgravity levels for payloads. Using the Option B (Freedom) truss segments and alpha joints will resolve this problem.

4. Use of the BUS-1 propulsion module will incur substantial modification and acquisition costs which have not been fully accounted for. Use of the Option A2 or B (Freedom) Propulsion modules will resolve this problem.

5. The role of Canada's robotic arm in space station operations has been dramatically diminished thus reducing the ability to manipulate objects on the truss. In addition, the controls for the arm have been deleted. Option A suggests that Canada absorb the substantial redesign costs and diminished role. Adding back the functionality contained in Option B (Freedom) would resolve this problem.

6. Option A's proposed logistics, resupply, and stowage capabilities and space shuttle utilization are out of balance and inadequate to supply and operate their proposed space station. Using the logistics carriers and shuttle systems in Option B (Freedom) will allow a proper balance to be attained.



Option A's Laboratory and Habitation modules have substantial weight problems which will be further aggravated by design work that has not yet been completed. Option A admits that at least 50% of the design work must be redone on these modules. Once their design is complete, these modules will be far too heavy to be lofted into orbit by the current space shuttle. Option A claims to save $100 Million by combining the two elements and cutting several shuttle flights. However, in acknowledging that serious weight threats may exceed the current space shuttle lifting capability, they readily admit that the lightweight Aluminum-Lithium tank is needed to provide the lift capability for the overweight modules. Development of this tank will cost $300 million. Option A would then be in the position of spending $300 million to save $100 million, a net increase of $200 million. This cost has not been included in Option A. The impacts on higher inclination orbits with the corresponding weight penalties should be obvious. Option B (Freedom) modules and nodes were optimized to be carried into orbit without modifications to the current space shuttle configuration.

Russian docking adapter loads have not been accommodated by Option A. Late in the redesign process, Option A was directed to use the Russian Soyuz docking Adapter (APAS) and attach it to the Pressurized Mating Adapter (PMA) located on the end of the laboratory and habitation modules The APAS requires 3000-4000 lbs of impact force in order to lock and capture. The PMA can only support 400-500 lbs of impact force during docking - roughly 1/10th of that required with the APAS. In addition to the additional 700 pound weight of the APAS, the PMA must be strengthened to accept these increased loads. This will add even more weight to the Laboratory and Habitation Modules.

Launch loads of the Russian docking adapter and associated hardware have not been accommodated by Option A. The end of the Laboratory and Habitation modules have not been strengthened to withstand the loads which will be encountered during launch imposed by the APAS and PMA which will be attached to these modules. In addition, the Laboratory module will attach to the truss at one end. The ends of this module will likely need reinforcement as well to withstand these loads. In both cases additional strengthening of these modules adds to their overall weight.


Background: Option A retains the truss concept used in Space Station Freedom wherein number of truss segments are launched and connected in space. Various portions of the space station are then attached to this backbone. Each segment is unique and is optimized for its specific location and function. Option A1 deletes 4 truss segments while Option A2 deletes 2 segments. In both designs, the connections between remaining segments are substantially altered. Both A1 and A2 alter the equipment attached to each segment, and remove a large rotating alpha joint used in the Freedom design to position the solar arrays. Option A1 adds a new propulsion unit to one end of the truss.

Each truss segment is currently optimized for weight and interconnections with other segments and hardware. Any change, such as consolidating equipment onto fewer truss segments, requires a complete redesign of the entire truss structure. The 6-12 month effort which will be required to bring Option A up to the same level of maturity present in Option B (Freedom)' will cost $1-2 billion. This equals or exceeds the money saved from deleting the truss segments in the first place.

The Option A truss configuration places the solar arrays too close together to allow the space shuttle to dock. Option A2 is configured such that the Japanese Module's exposed facility platform for payloads will be sprayed by shuttle rockets each time the shuttle arrives and departs.

Removing truss segments bring the solar arrays closer in, significantly increasing plume loads. The lack of fully articulating solar arrays prevents feathering and increases plume impingement from the shuttle during approach and departure and from the propulsion modules during reboost.

Altered solar array locations requires Option A to use more propellant for reboost. To minimize this aspect of Option A's design, reboost in arrow mode requires more propellant due to the necessary aiming thrusters in less than optimal directions (canting) to reduce plume impingement on the solar arrays.

Attaching Option A's new common module to the truss requires a complete redesign of the truss-to-module attachment structure. It also eliminates the prepackaged utility connectors, thus adding to the spacewalk (EVA) time required to attach the lab to the truss.

Option A must re-do all of the induced environment analysis (loads, thermal, vibration, etc.) to ensure the new design will actually work. The truss does not have a plasma contactor to prevent charge buildup present on Option B (Freedom). A negative charge buildup will result which will attract ions and erode critical hardware items. This item must be added at additional cost. The tighter packing which Option A's design imposes will especially complicate the passive and active thermal control of all truss mounted equipment, with and without the space shuttle docked. As with any new design, such analysis will uncover many problems, each with its own yet to be determined price tag.

Option A's condensed truss does not have sufficient clearance and space for all of the equipment and activities it will be required to perform. The starboard thermal radiator cannot clear truss segment S3 during rotation. Also, the ability to install the Canadian robotic arm on Flight 2 is questionable. At best, providing the space and clearances for attached payloads, EVA, robotics, Unpressurized Logistics Carriers, and a hundred other items will require a complete redesign of the truss.

At worst, Option A will have to add back some or all of the deleted truss segments in order to allow it to perform needed functions. Doing so would move Option A back to the baseline it supposedly had simplified - the key selling point to Option A.

Option B (Freedom) had already solved these clearance, packaging, interconnection, environmental, and load problems. All truss segments had either reached or were months away from their final design review hence the beginning of manufacture.


Option A deletes the alpha joints from the truss. In Option B (Freedom), alpha joints allow the solar arrays to revolve once per orbit to maximize solar illumination (hence power levels) while leaving the rest of the space station in a constant orientation. This constant orientation is optimized for micrometeoroid and debris shielding, microgravity levels, and payload viewing while minimizing atmospheric drag.

Deletion of alpha joints reduces power generation. Without alpha joints, the Option A design is forced to constantly reorient so as to maximize power generation and minimize drag. The lack of fully articulating solar arrays reduces total power generation. The available power to payloads is decreased by 10 kW from that achievable by Option B (Freedom) on an average basis.

Deleting alpha joints limits payload viewing and increases the risk of debris damage. The lack of fully articulating solar arrays to track the Sun force Option A to use an "arrow" attitude (truss pointed in the direction of travel (or the "velocity vector") to achieve acceptable power levels. By forcing the space station to fly in arrow mode, payload location on the truss facing the direction of flight is not possible . This precudes materials exposure research. Flying in arrow mode also increases the probability of radiator damage from micrometeoroid and orbit debris impact thus forcing the addition of additional shielding - and weight.

Reprientation of Option A design causes a substantial decrease in payload operations. To maintain power, Option A must rotate 90 degrees about the truss once every 52 days. These attitude flips reduce microgravity experiment time when coupled with the quiescent period cycle. The 90 degree attitude flips reduce yearly attached payload experiment time by approximately 30%.

Option A's attitude flips seriously affect communication capability. The 90 degree attitude flips reduce yearly space station communications coverage. Blockage from Option A's unique configuration of pressurized modules further reduces communication coverage. This reduces overall communication coverage by 30-60%. Such a reduction severely reduces space station system and experiment data relay.

Deleting the alpha joints will result in a totally new design of the truss segments that once contained these structures. To partially offset complaints about decreased power, viewing, and microgravity, Option A personnel have discussed a partially rotating joint - again, one which has yet to be designed or costed. Yet 60 % of the cost of the alpha joints in Option B (Freedom) has already been spent and the design is ready for manufacture. It is cheaper to finish with Option B (Freedom) than to depart on a wholly new design.


Option A limited the number of payload racks in the US laboratory module to 9, a 30% decrease in usable volume from that available in Option B (Freedom). In addition, Option A does not provide nearly enough volume for all stowage needs. No integrated stowage assessment has been done or costed. Option A representatives state that if additional volume is need for general stowage, that additional payload volume will be sacrificed to provide stowage. Preliminary analyses suggest this could amount to 2 to 3 racks. Meanwhile, payloads must continue to use their own volume to accommodate their stowage needs.

Option A deleted the Microgravity Sciences Glovebox. The only workstation proposed is an open work surface tray which is temporarily attached to racks. A tent can be added to keep things from floating away. Early operations aboard the space station will focus on microgravity and materials science at the direction of Congress and numerous advisory panels. The Microgravity Sciences Glovebox is pivotal to this research. Option A does not even attempt to come close to providing this capability.

Option A deleted the EXPRESS racks program. Space station users have long requested that a simplified means of placing payloads aboard the space station be implemented. The EXPRESS program was initiated to meet this need last year. By not implementing EXPRESS, Option A contradicts the expressed wishes of a clear majority of space station users.

Option A deleted Laboratory Support Equipment & General Laboratory Support Facilities. None of the refrigerators, measuring devices, and handling instruments needed to perform payload operations are included in this option. To make the space station useful they must be added back at additional cost and weight.

Option A does not specify whether the existing International Standard Payload Rack (ISPR) agreements between the US, Japan, Europe, and Canada will be maintained. Specifically, Option A does not define individual payload rack location power and thermal capabilities. Data Management System (DMS) specifications for payload locations are wholly lacking.

Option A has no dedicated truss attached payload sites. The Redesign Team Final Report states that Option A1 has 21 attached payload positions when complete. Option A design does not specify where all of these locations are nor does it specify the capabilities of the locations that are identified. Many sites are described as being "potentially" available for payload use. The 3-4 "potential" sites that have been identified by Option A are shared with the EVA and robotics systems. In fact, the truss sites lie directly within the maintenance corridor and must be moved every time the robot walks down the truss. This would cause repeated, total shutdown of payloads which are intended to operate for prolonged periods. Option A requires new hardware, not included in the Option A cost estimates, to accommodate attached payloads on the truss. No on-orbit parking locations are provided on the truss for the Unpressurized Logistics Carrier. The Option A- suggested solution could eliminate the few remaining external payload accommodations

Option B (Freedom) has fully identified and characterized the capabilities of its internal and external payload accommodations and supporting hardware such that payload design and scheduling has begun.



Option A's Utilization Flight manifests are inconsistent with planned on-orbit resources and insufficient for payload operation. Examples: Utilization Flight-2 (UF-2) carries a totally unpressurized payload at a time in the assembly sequence when there are no on-orbit accommodations available for that payload. In addition, Option A limits its payload resupply rack delivery to an average of 2 per resupply flight. This is a decrease of 59% (17 to 10) from Option B (Freedom), 4 times as large a reduction as the decrease in payload volume on orbit (15%) at completion. Fewer payload racks get disproportionately less resupply per rack than before.

Option A does not include costs to outfit the Mini-Pressurized Logistics Module (MPLM). Option A uses a modified version of Freedom's MPLM. The MPLM 's main structure is to be provided by Italy under existing agreements. The internal systems were to be provided by the US from the same development program which would have provided the Pressurized Logistics Module (PLM). Option A deleted the PLM and with it all of the internal systems the MPLM was to use. These costs to develop systems for the MPLM must be added to Option A's cost profile.

Option A's design for the 12-rack MPLM has an insufficient number of refrigerators and freezers. Option A proposes 2 active locations in the MPLM. These refrigerator units were to be developed for the PLM and have not been included in Option A's costs. Both of these refrigerator units will be filled with crew supplies. This completely precludes the transport of perishable payload materials in the MPLM and places severe constraints on the space shuttle middeck's already limited capability to transport these materials to and from orbit. Solutions would be to either modify the MPLM or the space shuttle middeck - both solutions would incur costs which have not been included in Option A's budget.

Option A assumes that additional on-orbit storage will be provided by an Italian Closet Module at no cost to the US. A quid pro quo between the US and Italy is assumed but not specified or costed. Suggested options include giving up US payload accommodations within US-provided laboratories to Italy thus further diminishing resources available to US investigators. The projected size of the closet module is also inadequate. Even after Option A's claim of having reduced spares by 30% reducing 15 days worth of supplies for safe mode and shuttle launch delay; the closet module would have to grow to 16 racks a cost impact not covered. As is the case with the MPLM, deleted, PLM-developed systems would be used to outfit this closet module. These systems have not been costed by Option A.

Option A's weight reserves are inconsistent with the lessons learned from a decade of space shuttle operations. Contingency weight/volume reserves such as the Program Manager's reserve have already been released in order to provide reasonable upmass for utilization during the assembly phase. No margin is left to cover contingencies. The Post-PHC (Permanent Human Capability) logistics flight manifest does not allow for flight hardware weight growth except by reducing the weight reserves held by the space shuttle program reserves i.e. zero margin for cargo weight growth - a historical feature of shuttle operations.


Option A has overstated the crew time available for science and ignored the need for station operations. Option A limits space shuttle crews to 4 during the tended phase of operations. Under this scenario, 1 crew member will stay on the space shuttle at all times in case the need for emergency departure arises. Option A personnel claim that they have approval to allow this crew member to be sleeping while performing this function. The Option Assessment and Evaluation section of the Redesign Team's final report claims that between "3+ and 3" crew members will be available for science functions under Option A during tended operations. No accounting for station operations has been included.

During tended operations, the space shuttle toilet is the only waste management system available. Should that fail, the crew must use bags or terminate the mission. In addition, the cost of this toilet (still under development) is currently listed against the space shuttle EDO (Extended Duration Orbiter) program - not against Option A. There are also $45 million worth of EDO modifications needed to be made to space shuttle orbiter OV-103 which were also not included in Option A cost reports.

The space shuttle flight manifest presented by Option A does not include the weight impacts required by the cryogenic hardware needed for assembly and utilization flights. This amounts to adding between 4 and 5 full tanks with weights ranging from 866-to 2400 lbs.


Option A EVA budgets are incomplete. Approximately 1800 lbs must be added to space shuttle missions which did not include the required maintenance EVA.

Option A does not have truss locations for the Unpressurized Logistics Carrier (ULC). Without the temporary storage space provided by the ULC, astronauts cannot maintain the space station after PHC.


Due to altered module pattern, the debris environment encountered by Option A's design is worsened causing ESA and NASDA modules to add additional shielding which results in weight and costs. In addition, Option A's design has insufficient EVA clearances for the European APM. If Option A-induced changes cause the European and Japanese modules to exceed baseline space shuttle capabilities, additional, uncosted redesigns will be needed with the burden placed upon our international partners.


The design and function of the Canadian Robotic Arm has been diminished to a point where its role in space station operations is minimal. In addition, the control work station for the arm has been deleted. The Canadian SSRMS (Space Station Remote Manipulator System) played a key role in the design of Space Station Freedom by being the prime means whereby payloads and resupply cargo were manipulated outside the space station. Option A proposes that development of a portable controller be done by and at the expense of Canada. Similarly the design of the arm must also be radically changed - again, at the expense of Canada. Adding the arm back to the Option A truss design will cause further design modifications to truss segments and will likely prohibit the use of most of the proposed attached payload locations. Using the Option B (Freedom) truss and arm design will alleviate this problem.

Option A's deletion of the Canadian Mobile Transporter requires 10 additional grapple fixtures and associated support structure on the truss. If Option A were to add back the Canadian Mobile Transporter, the S1 truss segment packaging problem would be made even worse than it already is by further restricting clearances.

For Flight 2, deleting the Mobile Transporter and the S2 truss segment prevents the SSRMS from placing the propulsion modules on the SSF. Modifying an existing piece of hardware can allow the placement of one of the two propulsion module, but requires more development money. This defect places the SSF at severe risk of re-entry.


Option A does not describe how it accommodates a centrifuge. Option A states that it accommodates a 2.5 meter Centrifuge at PHC and shows a module labeled "Centrifuge". In a letter dated 12 May 1993 to the head of the redesign team, Option A personnel stated that "In concept, a Centrifuge is being considered for accommodation. However, our task is to define the basic space station and we have not addressed the addition of a Centrifuge, in detail, although we have allocated a port for its potential location".

As is the case with the MPLM and Closet modules, outfitting of this module is to be provided by the US. No costs are included for this outfitting. Nor is any description of what sort of Centrifuge hardware will be accommodated i.e. the current 2.5 Centrifuge Facility and associated racks under development by NASA ARC. In addition, no mention is made of how the costs will be handled that are associated with any Option A-induced changes to the current Centrifuge Facility design, one which was scheduled to award Phase C/D contract in mid-1993.


Substantial BUS-1 implementation costs on the order of $1 billion are not included in Option A. Option A relies heavily on the use of BUS-1, a propulsion stage developed by Lockheed Corporation and already in use in classified DoD programs. An additional $180 million will be needed to modify BUS-1 to conform with space station requirements. If BUS-1 is utilized and the full purchase price is charged to NASA, the two units required by Option A would cost $992 million. None of these additional costs are included in the Option A cost summary.

BUS-1 change out prevents payloads from operating Option A1 switches the end of the truss that points to ram every three years when it swaps out the BUS-1 for replacement. Since most experiments are attitude dependent, this "ram swap" prevents operation of most payloads.

BUS-1 cannot be used if alpha joints are added to Option A. Adding an alpha joint would provide fully articulating solar arrays. However, the BUS-1 modules located on the ends of the truss cannot control the space station with an alpha joint in the truss.

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This page contains a single entry by Keith Cowing published on July 4, 1993 4:59 PM.

Letter From Dan Goldin to John Gibbons About Space Station Alpha is the next entry in this blog.

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