A suburban Washington insurance broker is donating $500,000 personal-accident policies to each of the five astronauts scheduled to blast off next month on the shuttle Doscoveryk. Corroon & Black Inspace Inc. donated a $1 million policy to Christa McAuliffe before the New Hampshire schoolteacher and six astronauts were killed in the Challenger explosion 2 1/2 years ago. Corroon & Black officials say they paid the McAuliffe family within 26 hours of the disaster. The insurance firm said Monday it will obtain the policy through a syndicate headed by Lloyd's of London. Corroon & Black is not disclosing the cost of the policy, although the company said premiums have risen sharply since the Challenger explosion.