After the Nostromo detects a signal from a potentially intelligent alien, the crew are arguing what to do about it. Most of the crew want to ignore it and return home, but Ash (Science Officer) reminds them that they signed a contract in which they agreed to investigate such signals or forfeit their entire 'share' of the operation.
Just after landing on LV-426, the ship is damaged and the mechanics are busy repairing it. Ripley is flitting about (I forget where). Dallas & Ash are discussing the signals and visiting their source. Kane joins them, while Lambert the Navigator sits at one of the more distant consoles in the cabin sucking down a cigarette in a desultory manner, listening.
Kane: I'll volunteer to be in the first group to go out.
Captain Dallas: Yeah that figures. ..You too Lambert.
Lambert: (nods resignedly, says sarcastically) ..swell
It turned out that Dallas was the other member of a 3 person group to 'suit up' for the trip. First it surprised me that Captain Dallas would allow the 2 most senior officers (himself and Kane, the Executive Officer) on-board to leave the shuttle, but we'll let that pass for the moment.
What absolutely astonished me was that Ash was not a member of the team. Who better than the Science Officer to assess and analyze what they found?
During the sojourn on the planet, Ash sits in a very important looking section of the shuttle surrounded by consoles and communications devices (which quickly fail once the team enter the alien spacecraft). It is Ripley that seems the major user of the communications instruments in the first instance (she hails for local 'space services' before they realize the Nostromo is nowhere near Earth). The rest of what Ash is doing during the surface mission does not seem an especially technical role, not compared to the value a Science Officer could bring on the surface.
Ash himself might have had reasons for not wanting to go on the mission.
- Fear of becoming the host? No. He was many things, but not fearful.
- Knowledge that he is not, or might not be, a suitable host. Maybe. But then, it is unclear how much they knew about the aliens.
- There being no-one else he could rely on to override the air-lock security and get the alien back into the ship.
That last one is one very good reason for him to not want to go on the mission, but ultimately he was not invited to go and never consulted as to who should go.
Why did Captain Dallas not choose the Science Officer to go on a mission that would likely involve encountering an alien species? Why did no-one else (particularly Lambert - who was chosen, and obviously reluctant) question that decision?