ATS-4

ATS-4 (Applications Technology Satellite) also known as ATS-D was a communications satellite launched by NASA on August 10, 1968^[3] from Cape Canaveral through an Atlas-Centaur (AC-17) rocket.^[1][2]

ATS-4, Advanced Tech. Sat. 4, ATS-D, PL-683A, 03344

ATS-4
Mission type	Weather Satellite
Operator	NASA
COSPAR ID	1968-068A
SATCAT no.	03344
Mission duration	38 days
Spacecraft properties
Bus	HS-306
Manufacturer	Hughes Aircraft
Launch mass	305 kilograms (672 lb)[1]
Power	350 W (peak)
Start of mission
Launch date	August 10, 1968, 22:33:00 (1968-08-10UTC22:33Z) UTC
Rocket	Atlas SLV-3C Centaur-D (AC-17)
Launch site	Cape Canaveral[1] LC-36A[2]
End of mission
Disposal	August 10, 1968
Decay date	October 17, 1968 (1968-10-18)[3]
Orbital parameters
Reference system	Geocentric
Regime	LEO
Eccentricity	0.042372[2]
Perigee altitude	185.99 kilometres (115.57 mi)[2]
Apogee altitude	766.89 kilometres (476.52 mi)[2]
Inclination	29.141º [2]
Period	94.131 minutes[2]
Applications Technology Satellites ← ATS-3 ATS-5 →

Objectives

The objective of ATS-4 was to investigate the possibilities of a gravity gradient stabilization system (the method of stabilizing artificial satellites).^[3]

Features

The satellite has a cylindrical shape with a 142-centimetre (56 in) diameter and 183-centimetre (72 in) height (about 360 centimetres (140 in) considering the motor cover) with the surface covered by solar panels that generated a maximum of 350 W of power,^[4] and stabilized by gravity gradient. It was based on the Hughes Aircraft HS-306 bus.^[5]

Instruments

A total of four experiments were conducted during the mission:

• Microwave Transponder
• Gravity Gradient Stabilization
• Image Orthicon (Day/Night) Camera
• Ion Thruster

Mission

The Atlas and Centaur stages performed satisfactorily and placed the Centaur/ATS-4 in an elliptical parking orbit. However the Centaur stage failed to re-ignite after a 61-minute coast. The failure was determined to be freezing of the hydrogen peroxide supply lines to the Centaur engines.^[2]

High atmospheric drag due to the low altitude of the achieved orbit (186 km perigee) precipitated the orbital decay of the spacecraft. ATS-4 still achieved good results in some of the experiments, but the primary objective of achieving gravity gradient stabilization of a satellite was not reached.

ATS-4 reentered the atmosphere on 17 October 1968.^[3]