Rao and Aryabhata: Recording to Playback

Three different properties in the record

The Aryabhata history specifies tape recording at 256 bits/s, playback at ten times that rate, and telemetry at 137.44 MHz. It also distinguishes early payload power difficulties from the spacecraft’s long tracking history.

Bits per second measures data rate. Megahertz measures cycles per second; the carrier frequency alone does not provide a data rate without additional information about the communication system. Nor does a tracking interval establish how much useful scientific data were stored.

Sources for this section: [1]

Original buffer fixture

Invent a buffer containing 1,536,000 bits, recorded at the stated recording rate. Define playback as ten times that rate. Assume no recording during playback, no data compression and no headers. How much recording time does the buffer represent, and what ideal contact time empties it?

Now reserve 20% of each contact for overhead, leaving 80% for payload bits. A contact lasts 600 seconds. Calculate useful capacity, remaining bits and total contact time required. Finally, as a separate invented mode, allow continued recording during playback. Does the emptying time change? The actual spacecraft’s simultaneous-operation capability is not established by this fixture.

Sources for this section: [1]

Reference answer: conserve the bits

The buffer represents 1,536,000/256=6,000 seconds, or 100 minutes, of recording. Playback is 2,560 bits/s, so the ideal emptying time is 600 seconds, or 10 minutes. A hundred minutes of data do not require a hundred minutes of playback under this stipulated design.

With overhead, the useful rate is 0.80×2,560=2,048 bits/s. The 600-second contact sends 1,228,800 bits and leaves 307,200. Emptying the original buffer requires 750 seconds of total contact. If recording continues at 256 bits/s, the net drain is 2,048−256=1,792 bits/s and emptying instead takes about 857.14 seconds.

Each result follows from its declared mode. Adding a continuing inflow changes the conservation equation; it is not a minor rounding adjustment. The numbers do not establish actual memory capacity, flight schedules or a communication link’s error performance.

Sources for this section: [1]

Return to the engineering history

The record describes ground reception at several sites and a young engineering team developing multiple test models.

That institutional and hardware context is part of the answer. A statement about one rate is a specification, not a complete history of a successful contact. A useful note separates the stored quantity, the receiving opportunity, the operational mode and the evidence for which experiment was functioning.

Sources for this section: [1]