STIS has observing modes which are unsupported but are "available", upon consultation with a STIS Instrument Scientist and after approval of Phase II proposal. Usage of these modes requires justification and entails certain responsibilities and risks.
Some modes and methods of observing are inherently challenging or push the limits of what can be done with STIS. These include:
- Coronagraphic spectroscopy
- Coronagraphic imaging
- Coronagraphy with low inner working angles
- Slitless first-order spectroscopy
- Long-slit echelle spectroscopy
- Spectroscopy with the highest spectral resolution
- Precise slit orientation requiring accurate offset angles.
- Solar system observations
- High signal-to-noise observations
HST has the ability to do simultaneous parallel observations. STIS can be used in combination with another instrument, as either the primary instrument pointing at the target position or the parallel instrument pointing at an offset position determined by the spacecraft geometry. Restrictions on parallel observations are given in the HST Call for Proposals.