Astro convention

Astro is a contract bridge bidding convention used to intervene over an opponent's one notrump (1NT) opening bid. The name is derived from the initials of the surnames of its inventors - Paul Allinger, Roger Stern and Lawrence Rosler.

Astro employs a 2-level overcall in a minor suit when holds an unbalanced hand with at least nine cards in two suits, at least one of which is a major; hand strength should be unsuitable for, or not strong enough for a penalty double, typically no more than 15 points. The minor suit overcalls are artificial and carry the following meanings:
 * 2 shows at least 5-4 or 4-5 length in hearts and a minor suit, and
 * 2 shows at least 5-4 or 4-5 length in spades and another suit.

When playing Astro but not holding the prescribed two-suited hand, the following calls are available over the 1NT opening by the opponents:
 * an overcall of 2 or 2 is natural showing a single-suited hand
 * Double is for penalties

Subsequent bidding
For purposes of subsequent bidding, the major suit indicated by the Astro Intervenor is termed the “anchor major”; the cheapest unbid suit is called the "neutral" suit. Depending upon action taken by the responder to the 1NT opener, Advancer may:
 * Pass when weak and holding six cards in the minor bid by the Intervenor, or
 * Raise the anchor major: (a) to the 2 level with at least 3-card support, preferably with an honour, and no game intentions, or (b) raise to the 3 level with at least 4-card support and inviting game, cognizant of vulnerability and the point range of the 1NT opening, or (c) raise to the 4 level with at least 4-card support for game-try, or
 * Bid an artificial and forcing 2NT to show some support in the anchor suit, game interest but no potential to bid further, or
 * Bid a new suit take-out or new suit jump, to show a 6-card or longer suit, or
 * Make a negative bid of 2 in the neutral suit to indicate having no other options, usually less than 3 cards headed by an honour in the anchor suit and at least a doubleton in the neutral suit.

Intervenor rebids include:
 * Pass after a neutral response with five cards in the neutral suit, or
 * a bid of the anchor major to show 5 cards, or
 * a bid of the second suit at the 3-level to show 6 cards and good playing strength.

Variations
In the following variations of Astro, the overcalls indicate more specific information about suit combinations:

Modified Astro

 * 2 shows a long heart suit with or without a long minor
 * 2 shows spades and a minor suit
 * 2 shows hearts and spades

Pinpoint Astro

 * 2 shows hearts and clubs
 * 2 shows hearts and diamonds
 * 2 shows hearts and spades
 * 2 shows spades and a minor suit
 * 2NT shows both minors

Roth-Stone Astro

 * 2 shows clubs and spades
 * 2 shows diamonds and spades
 * 3 shows clubs and hearts
 * 3 shows diamonds and hearts
 * Double shows hearts and spades against a strong 1NT opening; against a weak 1NT, it is penalty oriented showing at least 15 high card points.

Defense against Astro
Responder to the 1NT opener may:
 * Double with holdings in the anchor suit and in the minor overcalled, or
 * Cuebid the anchor suit when the hand is unsuited to defense, or
 * Pass, waiting, or
 * Bid a natural 2NT, invitational to game.

Alternative conventions
Several other bidding conventions use a variety of schemes to compete against a 1NT opening; these include: Aspro, Asptro, Brozel, Cappelletti, DONT, Landy and Ripstra.