Examples of Current Spacecraft

We conclude this chapter with some examples of current unmanned spacecraft and their applications areas. The main features and subsystem areas (see Table 7.1) of these satellites are shown in figures and described in tables. To put the mass of these spacecraft into perspective, it is helpful to bear in mind that 1000 kg is a metric tonne; a typical automobile weighs about to 1V2 metric tonnes, and a double-decker bus weighs about 10 metric tonnes. Because the life span of these spacecraft is short, the ones cited here will be relegated to history in a few years. But this book would be incomplete without giving the reader an idea of the mass, size, and appearance of currently flying spacecraft. The particular satellites chosen to represent the different application areas are as follows:

• Communications: Intelsat 8 (Fig. 7.3 and Table 7.3)

• Remote sensing: SPOT 5 (Fig. 7.4 and Table 7.4)

- Observatory: Hubble Space Telescope (Fig. 7.5 and Table 7.5)

- Interplanetary exploration (Cassini/Huygens; Fig. 7.6 and Table 7.6)

Figure 7.3: Artist's impression of the Intelsat 8A communications satellite in geostationary Earth orbit. (Image courtesy of Lockheed Martin.)

Table 7.3: The main features of the Intelsat 8 spacecraft

Description:

Launch mass:

Dry mass (without fuel):

% of launch mass: Fuel mass:

% of launch mass: Approximate size: Orbit type: Height: Inclination: Power (beginning of life): Payload Mass:

Mass (% of dry mass): Performance:

Intelsat 8 spacecraft is a typical geostationary Earth orbit

(GEO) communication satellite, providing predominantly an intercontinental telephone communication service.

3250 kg

1540 kg

1710 kg

35,790 km 0 degrees

460 kg (estimated) 30% (estimated)

The communications payload can carry typically 22,000 telephone calls and 3 color TV broadcasts simultaneously

Figure 7.4: Artist's impression of the SPOT 5 Earth observation satellite in a near-polar low Earth orbit. (© CNES/ Artist David Ducros.)

Table 7.4: The main features of the SPOT 5 spacecraft

Figure 7.4: Artist's impression of the SPOT 5 Earth observation satellite in a near-polar low Earth orbit. (© CNES/ Artist David Ducros.)

Description:

Launch mass:

Dry mass (without fuel):

% of launch mass: Fuel mass:

% of launch mass: Approximate size: Orbit type: Height: Inclination: Power (beginning of life): Payload Mass:

Mass (% of dry mass): Performance:

The SPOT series of spacecraft was developed as a French national space program. The spacecraft were designed and manufactured by the French space agency CNES (Centre National d'Etude Spatiales). 2760 kg 2600 kg 94% 160 kg 6%

2 x 2 x 5.6 m Near polar LEO 822 km 98.7 degrees 2.5 kW

1400 kg 54%

Provides images of the ground that are 120 km across, with a resolution of 10 m

Figure 7.5: Photograph taken by shuttle astronauts of the Hubble Space Telescope in a near-equatorial low Earth orbit. (Image courtesy of National Aeronautics and Space Administration [NASA].)

Table 7.5: The main features of the Hubble Space Telescope

Description:

Named after Edwin Hubble, who discovered the expan

sion of the universe in the 1920s, this orbiting telescope

has revolutionized all aspects of observational astronomy.

Launch mass:

10,840 kg

Dry mass (without fuel):

10,840 kg

% of launch mass:

100%

Fuel mass:

0 kg

% of launch mass:

0%

Approximate size:

A cylinder 13 m long x 4.3 m diameter

Orbit type:

Low inclination LEO

Height:

Approximately 600 km

Inclination:

28.5 degrees

Power (beginning of life):

5 kW

Payload

Mass:

1450 kg

Mass (% of dry mass):

13%

Performance:

The main element of the telescope is a mirror 2.4 m in

diameter that can see objects just 120 m across on the

moon's surface

Figure 7.6: The Cassini/Huygens spacecraft configuration. The spacecraft entered orbit around the planet Saturn in July 2004. (Artist's impression by David Seal. Backdrop image courtesy of NASA/Jet Propulsion Laboratory [JPL]—Caltech.)

Table 7.6: The main features of the Cassini/Huygens spacecraft

Description:

Launch mass:

Dry mass (without fuel):

% of launch mass: Fuel mass:

% of launch mass: Approximate size: Orbit type: Height:

Inclination: Power (beginning of life): Payload Mass:

Performance:

The spacecraft is made up of two main parts: Cassini, which is the Saturn orbiter built by NASA, and the Huygens probe built be the European Space Agency (ESA). The Huygens probe successfully landed on Saturn's moon Titan in January 2005. 5630 kg

3140 kg

6.8 m high, with a 4-m communications dish Saturn orbit

Orbit height continuously modified using swing-bys around Saturn's moons

Near-equatorial

815 W (using RTGs; see power section in Chapter 9) 670 kg [330 kg (orbiter payload) + 340 kg (probe)] 31%

The images of Saturn and its moons have been particularly spectacular!

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