The Hitchhiker Project

NASA's Hitchhiker project began in early 1984. It was created to accommodate small attached payloads in the space shuttle payload bay. Hitchhikers are intended for customers whose space activity requires power, data or command services.

The first Hitchhiker launched on STS-61-C on January 12, 1986. Called HHG-1, it was mounted to the side of the payload bay and carried three experiments. The second Hitchhiker launched on STS-39 on April 28, 1991. This payload was called Space Test Payload (STP)-1 and consisted of five experiments mounted onto a cross-bay carrier. Between 1992 and 1995, 12 Hitchhikers are manifested to fly on the space shuttle.

The Hitchhiker system provides real-time communications between the payload and customers in the Hitchhiker control center at Goddard Space Flight Center, Greenbelt, Md. The system also can provide crew control/display capability, if necessary. Hitchhikers were created to provide a quick reaction and low cost capability for flying small payloads in the shuttle payload bay.

Along with NASA's Get Away Specials (GAS), Hitchhiker is developed and operated by the Goddard Space Flight Center Shuttle Small Payloads Project (SSPP). Unlike Hitchhikers, GAS payloads are only mounted in canisters, do not connect to orbiter electrical services and do not require significant shuttle support.

Hitchhiker Experiments

Hitchhiker experiments are housed in canisters or attached to mounting plates. The Hitchhiker canister comes in two varieties--the Hitchhiker Motorized Door Canister and the Sealed Canisters. The Hitchhiker Motorized Door Canister has mechanical interfaces nearly identical to a GAS canister and can accommodate a customer payload of up to 160 pounds (72.6 kilograms). This canister allows a payload to be exposed directly to the environment of space.

The Sealed Canister, without a door, can accommodate a customer payload up to 200 pounds (90.7 kilograms). The payload in this canister is sealed in an atmosphere of nitrogen or air.

Experiments attached to mounting plates may be placed on the vertical plate, a 25 inches (63.5 centimeters) by 39 inches (99.1 centimeters) mounting surface for up to 200 pounds (90.7 kilograms) of customer hardware. A larger mounting plate measures 50 inches (127 centimeters) by 60 inches (152.4 centimeters). This plate, available for use on the side-mount carrier, is for larger experiments or hardware requirements. Customer hardware mounted on plates may need additional customer-provided thermal control provisions, such as heaters or blankets.

The Hitchhiker Carrier System

The Hitchhiker carrier system is modular and expandable in accordance with payload requirements. This flexibility allows maximum efficiency in utilizing orbiter resources and increases the potential for early manifesting on the shuttle.

There are two types of carrier systems--the Hitchhiker Side-Mount Carrier System and the Hitchhiker Cross-Bay Bridge Carrier System. Either system can accept the Hitchhiker canister and the mounting plates.

The Hitchhiker Side-Mount Carrier System uses a GAS Adapter Beam for all equipment. The beam attaches to the orbiter frame. The side-mount carrier is usually installed in the forward starboard side of the payload bay, although other configurations and locations are possible. This carrier can hold up to three experiments and the Hitchhiker avionics box, which connects the power, data and signal from the shuttle to the experiments.

The Hitchhiker Cross-Bay Carrier can be located anywhere in the payload bay. The carrier can accommodate 11 Hitchhiker canisters or 11 of the smaller mounting plates. There is also room for the necessary avionic units.

Four additional mounting slots are located on the top of the carrier and can accept 33 inch (83.8 centimeter) by 27 inch (68.6 centimeter) pallets or 33 inch (83.8 centimeter) by 55 inch (139.7 centimeter) pallets in any combination with up to 500 pounds (226.8 kilograms) of equipment. Any customer experiments and hardware that can be mounted on the side-mount carrier can also be flown on the cross-bay carrier.

Astronaut Involvement

NASA created Hitchhikers to provide customers with a way to send small payloads into orbit on the space shuttle. This is done with a short turn-around-time--from manifest to flight takes an average of 18 months. To keep the project on schedule, experiments need to fit in canisters or on mounting plates and meet standard mechanical and electrical interfaces.

Because the payload meets these conditions, it also is entitled to special "handling" in the orbiter that other small payloads, like the Get Away Specials do not receive. This special handling includes tapping into the shuttle for power and "astronaut" services,"such as requiring specific shuttle attitudes or maneuvers. The orbiter crew moves the shuttle when necessary to the position needed for the Hitchhiker experiment, provided it does not interfere with he needs of the primary payloads.

Hitchhikers are manifested to fly with primary payloads that either have similar requirements or that will not be affected by the changes in shuttle position necessary to the Hitchhiker experiments. In addition to making adjustments to the orbiter, the astronaut crew participates in the Hitchhiker experiments by controlling the flow of orbiter power on or off using two switches located on the Standard Switch Panel.

The first switch controls power to the avionics unit. The second switch allows power to flow from the avionics unit to the experiment. This simple measure allows the astronauts to have some control over the experiment, in the event of a problem. For some payloads, the crew has a keyboard/display unit, for additional control.

Avionics

Getting the power from the shuttle to the payload requires an avionics unit. This unit connects the power from the shuttle to the experiment. The avionics unit also carries the equipment for transmitting the data real-time to the ground control center. The avionics unit also contains the relay switching equipment and has the connections for the customer to use the shuttle television system, and the crew control/display system. Each avionics unit can handle the requirements for six experiments.

The Goddard Connection

Goddard is responsible for the management and operation of the Hitchhiker project through the Shuttle Small Payloads Project. In this capacity Goddard provides the Hitchhiker carriers and the avionics unit.

During the mission, customers use a control center located at Goddard. The customer provides Ground System Equipment (CGSE), software and personnel to generate commands to the payload and display data from the payload during flight, as well as during payload-to-carrier integration and verification testing.

The Hitchhiker carrier system is equipped with a "transparent" data system which allows customers to easily use their existing ground equipment and software to control their experiments during flight. Data is sent down to the control center in real time, but it also is recorded at Goddard once it reaches the ground. The data is transmitted over Goddard's Tracking and Data Relay Satellite System.