James R. Wertz, Microcosm, 5/11/06

At RS4 there seemed to be more definitions of Responsiveness than participants.  The purpose of this technical note is to give preliminary definitions of Levels of Responsiveness in terms of what it means in cost and preparation.

Levels of Responsiveness for systems to be launched

• Level 0 -- System ready, fueled, and on the pad or ship or in the plane on station and ready to launch on command.  All orbital computations done and loaded into ground and on-board computer

• Level 1 -- System integrated and on hold on the pad or ship, not yet fueled.  Can maintain this posture essentially indefinitely

• Level 2 -- System in storage;  payload and vehicle not yet integrated;  payload built and encapsulated in a LV fairing, may have some software uploads;  personnel on alert

• Level 2a -- Same as level 2, but personnel not on alert

• Level 3 -- Spacecraft largely assembled, but one or more plug-and-play modules built, but not yet incorporated

• Level 4 (“6-day spacecraft”) -- Plug-and-play modules built for both spacecraft and payload and ready for assembly and test based on newly defined mission requirements

Levels of Responsiveness for systems already on orbit

• Level 0 -- Willing to make a major maneuver (0.5 to 2 km/sec) to provide coverage at the desired place and time

• Level 1 -- Willing to make a minor maneuver (5 to 50 m/sec) to provide coverage at the desired place and time

• Level 2 -- No maneuver allowed for specific coverage;  will provide coverage of the desired location at the next available time

Discussion

It is not the case that on-orbit assets are necessarily more responsive than those on the ground.  One often thinks of a spacecraft as being comparable to an aircraft whose path and timing can be adjusted to meet the needs of the situation.  In fact, spacecraft are much more comparable to a speeding bullet (only much faster than any rifle bullet).  Their path and time of arrival can be changed, but only by a small amount and at great effort (= expense).  If we are looking for coverage of a specific location either as soon as possible (i.e., after a tsunami) or at a specified future time (i.e., attack coverage), then, from a technical perspective, this is more easily and cheaply done by launching from the ground, with the launch timing and spacecraft obit selected to meet the desired objectives.  For example, without a large delta V maneuver, Sun synchronous satellites traditionally used for surveillance will typically revisit a specific ground location every 3 or 4 days.  Satellites launched from the ground can be timed to be there when needed and can arrive within less than an hour (or possibly a few hours if time for orbit phasing or on-orbit check-out is required).